text: /*
   * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
   * Copyright (c) 2009-2012, Pieter Noordhuis <pcnoordhuis at gmail dot com>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   *   * Redistributions of source code must retain the above copyright notice,
   *     this list of conditions and the following disclaimer.
   *   * Redistributions in binary form must reproduce the above copyright
   *     notice, this list of conditions and the following disclaimer in the
   *     documentation and/or other materials provided with the distribution.
   *   * Neither the name of Redis nor the names of its contributors may be used
   *     to endorse or promote products derived from this software without
   *     specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
   * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   */
  
  /*-----------------------------------------------------------------------------
   * Sorted set API
   *----------------------------------------------------------------------------*/
  
  /* ZSETs are ordered sets using two data structures to hold the same elements
   * in order to get O(log(N)) INSERT and REMOVE operations into a sorted
   * data structure.
   *
   * The elements are added to a hash table mapping Redis objects to scores.
   * At the same time the elements are added to a skip list mapping scores
   * to Redis objects (so objects are sorted by scores in this "view").
   *
   * Note that the SDS string representing the element is the same in both
   * the hash table and skiplist in order to save memory. What we do in order
   * to manage the shared SDS string more easily is to free the SDS string
   * only in zslFreeNode(). The dictionary has no value free method set.
   * So we should always remove an element from the dictionary, and later from
   * the skiplist.
   *
   * This skiplist implementation is almost a C translation of the original
   * algorithm described by William Pugh in "Skip Lists: A Probabilistic
   * Alternative to Balanced Trees", modified in three ways:
   * a) this implementation allows for repeated scores.
   * b) the comparison is not just by key (our 'score') but by satellite data.
   * c) there is a back pointer, so it's a doubly linked list with the back
   * pointers being only at "level 1". This allows to traverse the list
   * from tail to head, useful for ZREVRANGE. */
  
  #include "server.h"
  #include <math.h>
  
  /*-----------------------------------------------------------------------------
   * Skiplist implementation of the low level API
   *----------------------------------------------------------------------------*/
  
  int zslLexValueGteMin(sds value, zlexrangespec *spec);
  int zslLexValueLteMax(sds value, zlexrangespec *spec);
  
  /* Create a skiplist node with the specified number of levels.
   * The SDS string 'ele' is referenced by the node after the call. */
  //创建一个层数level，分数为score，对象为obj的跳跃表节点
  zskiplistNode *zslCreateNode(int level, double score, sds ele) {
      //分配空间
      zskiplistNode *zn =
          zmalloc(sizeof(*zn)+level*sizeof(struct zskiplistLevel));
      zn->score = score;
      zn->ele = ele;
      return zn;
  }
  
  /* Create a new skiplist. */
  //创建返回一个跳跃表 表头zskiplist
  zskiplist *zslCreate(void) {
      int j;
      zskiplist *zsl;
  
      zsl = zmalloc(sizeof(*zsl));
      zsl->level = 1;
      zsl->length = 0;
      //创建一个层数为32，分数为0，没有obj的跳跃表头节点
      zsl->header = zslCreateNode(ZSKIPLIST_MAXLEVEL,0,NULL);
      for (j = 0; j < ZSKIPLIST_MAXLEVEL; j++) {
          zsl->header->level[j].forward = NULL; //将跳跃表头节点的所有前进指针forward设置为NULL
          zsl->header->level[j].span = 0; //将跳跃表头节点的所有跨度span设置为0
      }
      zsl->header->backward = NULL; //跳跃表头节点的后退指针backward置为NULL
      zsl->tail = NULL; //表头指向跳跃表尾节点的指针置为NULL
      return zsl;
  }
  
  /* Free the specified skiplist node. The referenced SDS string representation
   * of the element is freed too, unless node->ele is set to NULL before calling
   * this function. */
  //释放一个跳跃表节点
  void zslFreeNode(zskiplistNode *node) {
      sdsfree(node->ele);
      zfree(node); //释放该该节点空间
  }
  
  /* Free a whole skiplist. */
  void zslFree(zskiplist *zsl) {
      zskiplistNode *node = zsl->header->level[0].forward, *next;
  
      // 释放头结点
      zfree(zsl->header);
      while(node) {//释放其他节点
          next = node->level[0].forward; //备份下一个节点地址
          zslFreeNode(node); //释放节点空间
          node = next; //指向下一个节点
      }
      zfree(zsl); //释放表头
  }
  
  /* Returns a random level for the new skiplist node we are going to create.
   * The return value of this function is between 1 and ZSKIPLIST_MAXLEVEL
   * (both inclusive), with a powerlaw-alike distribution where higher
   * levels are less likely to be returned. */
  //返回一个随机层数值
  int zslRandomLevel(void) {
      int level = 1;
      while ((random()&0xFFFF) < (ZSKIPLIST_P * 0xFFFF))
          level += 1;
      return (level<ZSKIPLIST_MAXLEVEL) ? level : ZSKIPLIST_MAXLEVEL;
  }
  
  /* Insert a new node in the skiplist. Assumes the element does not already
   * exist (up to the caller to enforce that). The skiplist takes ownership
   * of the passed SDS string 'ele'. */
  //创建一个节点，分数为score，对象为ele，插入到zsl表头管理的跳跃表中，并返回新节点的地址
  zskiplistNode *zslInsert(zskiplist *zsl, double score, sds ele) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      unsigned int rank[ZSKIPLIST_MAXLEVEL];
      int i, level;
  
      serverAssert(!isnan(score));
      x = zsl->header;//获取跳跃表头结点地址，从头节点开始一层一层遍历
      for (i = zsl->level-1; i >= 0; i--) { //遍历头节点的每个level，从下标最大层减1到0
          /* store rank that is crossed to reach the insert position */
          rank[i] = i == (zsl->level-1) ? 0 : rank[i+1]; //更新rank[i]为i+1所跨越的节点数，但是最外一层为0
          //这个while循环是查找的过程，沿着x指针遍历跳跃表，满足以下条件则要继续在当层往前走
          while (x->level[i].forward && //当前层的前进指针不为空且
                  (x->level[i].forward->score < score || //当前的要插入的score大于当前层的score或
                      (x->level[i].forward->score == score && //当前score等于要插入的score且
                      sdscmp(x->level[i].forward->ele,ele) < 0))) //当前层的对象与要插入的obj不等
          {
              rank[i] += x->level[i].span; //记录该层一共跨越了多少节点 加上 上一层遍历所跨越的节点数
              x = x->level[i].forward; //指向下一个节点
          }
          update[i] = x; //while循环跳出时，用update[i]记录第i层所遍历到的最后一个节点，遍历到i=0时，就要在该节点后要插入节点
      }
      /* we assume the element is not already inside, since we allow duplicated
       * scores, reinserting the same element should never happen since the
       * caller of zslInsert() should test in the hash table if the element is
       * already inside or not. */
      level = zslRandomLevel(); //获得一个随机的层数
      if (level > zsl->level) { //如果大于当前所有节点最大的层数时
          for (i = zsl->level; i < level; i++) {
              rank[i] = 0; //将大于等于原来zsl->level层以上的rank[]设置为0
              update[i] = zsl->header; //将大于等于原来zsl->level层以上update[i]指向头结点
              update[i]->level[i].span = zsl->length; //update[i]已经指向头结点，将第i层的跨度设置为length
          } //length代表跳跃表的节点数量
          zsl->level = level; //更新表中的最大成数值
      }
      x = zslCreateNode(level,score,ele); //创建一个节点
      for (i = 0; i < level; i++) { //遍历每一层
          x->level[i].forward = update[i]->level[i].forward; //设置新节点的前进指针为查找时（while循环）每一层最后一个节点的的前进指针
          update[i]->level[i].forward = x; //再把查找时每层的最后一个节点的前进指针设置为新创建的节点地址
  
          /* update span covered by update[i] as x is inserted here */
          x->level[i].span = update[i]->level[i].span - (rank[0] - rank[i]); //更新插入节点的跨度值
          update[i]->level[i].span = (rank[0] - rank[i]) + 1; //更新插入节点前一个节点的跨度值
      }
  
      /* increment span for untouched levels */
      for (i = level; i < zsl->level; i++) { //如果插入节点的level小于原来的zsl->level才会执行
          update[i]->level[i].span++; //因为高度没有达到这些层，所以只需将查找时每层最后一个节点的值的跨度加1
      }
  
      //设置插入节点的后退指针，就是查找时最下层的最后一个节点，该节点的地址记录在update[0]中
      //如果插入在第二个节点，也就是头结点后的位置就将后退指针设置为NULL
      x->backward = (update[0] == zsl->header) ? NULL : update[0];
      if (x->level[0].forward) //如果x节点不是最尾部的节点
          x->level[0].forward->backward = x; //就将x节点后面的节点的后退节点设置成为x地址
      else
          zsl->tail = x; //否则更新表头的tail指针，指向最尾部的节点x
      zsl->length++; //跳跃表节点计数器加1
      return x; //返回x地址
  }
  
  /* Internal function used by zslDelete, zslDeleteRangeByScore and
   * zslDeleteRangeByRank. */
  //被zslDelete, zslDeleteByScore and zslDeleteByRank使用的内部函数
  //删除节点
  void zslDeleteNode(zskiplist *zsl, zskiplistNode *x, zskiplistNode **update) {
      int i;
      //设置前进指针和跨度
      for (i = 0; i < zsl->level; i++) { //遍历下标为0到跳跃表最大层数-1的层
          if (update[i]->level[i].forward == x) { //如果找到该节点
              update[i]->level[i].span += x->level[i].span - 1; //将前一个节点的跨度减1
              update[i]->level[i].forward = x->level[i].forward;
              //前一个节点的前进指针指向被删除的节点的后一个节点，跳过该节点
          } else {
              update[i]->level[i].span -= 1; //在第i层没找到，只将该层的最后一个节点的跨度减1
          }
      }
      //设置后退指针
      if (x->level[0].forward) { //如果被删除的前进节点不为空，后面还有节点
          x->level[0].forward->backward = x->backward; //就将后面节点的后退指针指向被删除节点x的回退指针
      } else {
          zsl->tail = x->backward; //否则直接将被删除的x节点的后退节点设置为表头的tail指针
      }
      //更新跳跃表最大层数
      while(zsl->level > 1 && zsl->header->level[zsl->level-1].forward == NULL)
          zsl->level--;
      zsl->length--;
  }
  
  /* Delete an element with matching score/element from the skiplist.
   * The function returns 1 if the node was found and deleted, otherwise
   * 0 is returned.
   *
   * If 'node' is NULL the deleted node is freed by zslFreeNode(), otherwise
   * it is not freed (but just unlinked) and *node is set to the node pointer,
   * so that it is possible for the caller to reuse the node (including the
   * referenced SDS string at node->ele). */
  //删除score和obj的节点
  int zslDelete(zskiplist *zsl, double score, sds ele, zskiplistNode **node) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      int i;
      //下面的循环类似于zslInsert的查找部分
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) { //获取跳跃表头结点地址，从头节点开始一层一层遍历
      //这个while循环是查找的过程，沿着x指针遍历跳跃表，满足以下条件则要继续在当层往前走
          while (x->level[i].forward &&
                  (x->level[i].forward->score < score ||
                      (x->level[i].forward->score == score &&
                       sdscmp(x->level[i].forward->ele,ele) < 0)))
          {
              x = x->level[i].forward;
          }
          //while循环跳出时，用update[i]记录第i层所遍历到的最后一个节点，遍历到i=0时，就要在该节点后要插入节点
          update[i] = x;
      }
      /* We may have multiple elements with the same score, what we need
       * is to find the element with both the right score and object. */
      x = x->level[0].forward; //获取x的后面一个节点
      if (x && score == x->score && sdscmp(x->ele,ele) == 0) { //如果是要被删除的节点
          zslDeleteNode(zsl, x, update); //删除该节点
          if (!node)
              zslFreeNode(x); //释放空间
          else
              *node = x;
          return 1;
      }
      return 0; /* not found */
  }
  
  /* Update the score of an element inside the sorted set skiplist.
   * Note that the element must exist and must match 'score'.
   * This function does not update the score in the hash table side, the
   * caller should take care of it.
   *
   * Note that this function attempts to just update the node, in case after
   * the score update, the node would be exactly at the same position.
   * Otherwise the skiplist is modified by removing and re-adding a new
   * element, which is more costly.
   *
   * The function returns the updated element skiplist node pointer. */
  // 更新score
  zskiplistNode *zslUpdateScore(zskiplist *zsl, double curscore, sds ele, double newscore) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      int i;
  
      /* We need to seek to element to update to start: this is useful anyway,
       * we'll have to update or remove it. */
      // 先查找
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          while (x->level[i].forward &&
                  (x->level[i].forward->score < curscore ||
                      (x->level[i].forward->score == curscore &&
                       sdscmp(x->level[i].forward->ele,ele) < 0)))
          {
              x = x->level[i].forward;
          }
          update[i] = x;
      }
  
      /* Jump to our element: note that this function assumes that the
       * element with the matching score exists. */
      x = x->level[0].forward;
      serverAssert(x && curscore == x->score && sdscmp(x->ele,ele) == 0);
  
      /* If the node, after the score update, would be still exactly
       * at the same position, we can just update the score without
       * actually removing and re-inserting the element in the skiplist. */
      // 满足条件更新
      if ((x->backward == NULL || x->backward->score < newscore) &&
          (x->level[0].forward == NULL || x->level[0].forward->score > newscore))
      {
          x->score = newscore;
          return x;
      }
  
      /* No way to reuse the old node: we need to remove and insert a new
       * one at a different place. */
      // 删除节点
      zslDeleteNode(zsl, x, update);
      // 插入新节点
      zskiplistNode *newnode = zslInsert(zsl,newscore,x->ele);
      /* We reused the old node x->ele SDS string, free the node now
       * since zslInsert created a new one. */
      x->ele = NULL;
      zslFreeNode(x);
      return newnode;
  }
  
  //value 是否大于（或大于等于）范围 spec 中的 min 项
  //如果返回1表示value大于等于min，否则返回0
  int zslValueGteMin(double value, zrangespec *spec) {
      return spec->minex ? (value > spec->min) : (value >= spec->min);
  }
  
  //value是否小于或小于等于范围 spec 中的max
  //返回1表示value小于等于max，否则返回0
  int zslValueLteMax(double value, zrangespec *spec) {
      return spec->maxex ? (value < spec->max) : (value <= spec->max);
  }
  
  /* Returns if there is a part of the zset is in range. */
  // //如果range范围包含在跳跃表的范围返回1，否则返回0
  int zslIsInRange(zskiplist *zsl, zrangespec *range) {
      zskiplistNode *x;
  
      /* Test for ranges that will always be empty. */
      // 排除错误范围，或0范围
      if (range->min > range->max ||
              (range->min == range->max && (range->minex || range->maxex)))
          return 0;
      //最高分
      x = zsl->tail;
      if (x == NULL || !zslValueGteMin(x->score,range))
          return 0;
      //最低分
      x = zsl->header->level[0].forward;
      if (x == NULL || !zslValueLteMax(x->score,range))
          return 0;
      //最大值大于min，最小值小于max且min小于max返回1
      return 1;
  }
  
  /* Find the first node that is contained in the specified range.
   * Returns NULL when no element is contained in the range. */
  //返回第一个分数在range范围内的节点
  zskiplistNode *zslFirstInRange(zskiplist *zsl, zrangespec *range) {
      zskiplistNode *x;
      int i;
  
      /* If everything is out of range, return early. */
      //如果不在范围内，则返回NULL，确保至少有一个节点符号range
      if (!zslIsInRange(zsl,range)) return NULL;
  
      x = zsl->header;
      //遍历跳跃表
      for (i = zsl->level-1; i >= 0; i--) { //遍历每一层
          /* Go forward while *OUT* of range. */
          while (x->level[i].forward && //如果该层有下一个节点且
              !zslValueGteMin(x->level[i].forward->score,range)) //当前节点的score还小于(小于等于)range的min
                  x = x->level[i].forward; //继续指向下一个节点
      }
  
      /* This is an inner range, so the next node cannot be NULL. */
      x = x->level[0].forward;
      serverAssert(x != NULL);
  
      /* Check if score <= max. */
      //该节点的分值如果比max还要大，就返回NULL
      if (!zslValueLteMax(x->score,range)) return NULL;
      return x;
  }
  
  /* Find the last node that is contained in the specified range.
   * Returns NULL when no element is contained in the range. */
  //返回最后一个分数在range范围内的节点
  zskiplistNode *zslLastInRange(zskiplist *zsl, zrangespec *range) {
      zskiplistNode *x;
      int i;
  
      /* If everything is out of range, return early. */
      if (!zslIsInRange(zsl,range)) return NULL;
  
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          /* Go forward while *IN* range. */
          while (x->level[i].forward &&
              zslValueLteMax(x->level[i].forward->score,range))
                  x = x->level[i].forward;
      }
  
      /* This is an inner range, so this node cannot be NULL. */
      serverAssert(x != NULL);
  
      /* Check if score >= min. */
      //如果找到的节点的分值比range的min还要小
      if (!zslValueGteMin(x->score,range)) return NULL;
      return x;
  }
  
  /* Delete all the elements with score between min and max from the skiplist.
   * Min and max are inclusive, so a score >= min || score <= max is deleted.
   * Note that this function takes the reference to the hash table view of the
   * sorted set, in order to remove the elements from the hash table too. */
  //删除所有分值介于min和max之间（包括min和max）的节点，并且将字典中的对象也删除(字典和跳跃表同时表示有序集合)
  unsigned long zslDeleteRangeByScore(zskiplist *zsl, zrangespec *range, dict *dict) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      unsigned long removed = 0;
      int i;
  
      //找到删除节点中的最小值的节点，大于等于min的
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          while (x->level[i].forward && (range->minex ?
              x->level[i].forward->score <= range->min :
              x->level[i].forward->score < range->min))
                  x = x->level[i].forward;
          update[i] = x; //记录要删除的节点的前一个节点的地址
      }
  
      /* Current node is the last with score < or <= min. */
      x = x->level[0].forward; //获得被删除节点的地址
  
      /* Delete nodes while in range. */
      //删除一直删到最大值的节点，该值小于等于max的
      while (x &&
             (range->maxex ? x->score < range->max : x->score <= range->max))
      {
          zskiplistNode *next = x->level[0].forward; //备份被删除节点的下一个节点
          zslDeleteNode(zsl,x,update);
          dictDelete(dict,x->ele); //将字典中的对象也删除了
          zslFreeNode(x); /* Here is where x->ele is actually released. */
          removed++;
          x = next;
      }
      return removed;
  }
  
  //删除字典序的范围range之间的节点，并且将字典中的对象也删除
  unsigned long zslDeleteRangeByLex(zskiplist *zsl, zlexrangespec *range, dict *dict) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      unsigned long removed = 0;
      int i;
  
  
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          while (x->level[i].forward && //当前层的前进指针不为空且
              !zslLexValueGteMin(x->level[i].forward->ele,range)) //obj对象字典序小于range的min
                  x = x->level[i].forward;
          update[i] = x; //记录要删除的节点的前一个节点的地址
      }
  
      /* Current node is the last with score < or <= min. */
      x = x->level[0].forward; //获得被删除节点的地址
  
      /* Delete nodes while in range. */
      while (x && zslLexValueLteMax(x->ele,range)) { //只要obj字典序还小于max就一直删除
          zskiplistNode *next = x->level[0].forward;
          zslDeleteNode(zsl,x,update);
          dictDelete(dict,x->ele);
          zslFreeNode(x); /* Here is where x->ele is actually released. */
          removed++;
          x = next;
      }
      return removed; //返回被删除的节点个数
  }
  
  /* Delete all the elements with rank between start and end from the skiplist.
   * Start and end are inclusive. Note that start and end need to be 1-based */
  //删除跳跃表中所有给定排位内的节点
  unsigned long zslDeleteRangeByRank(zskiplist *zsl, unsigned int start, unsigned int end, dict *dict) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      unsigned long traversed = 0, removed = 0;
      int i;
  
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          while (x->level[i].forward && (traversed + x->level[i].span) < start) { //还没到start起始的位置，则向前走
              traversed += x->level[i].span;
              x = x->level[i].forward; //指向下一个节点
          }
          update[i] = x;
      }
  
      traversed++;
      x = x->level[0].forward;
      while (x && traversed <= end) {
          zskiplistNode *next = x->level[0].forward;
          zslDeleteNode(zsl,x,update);
          dictDelete(dict,x->ele);
          zslFreeNode(x);
          removed++;
          traversed++; //更新traversed
          x = next;
      }
      return removed;
  }
  
  /* Find the rank for an element by both score and key.
   * Returns 0 when the element cannot be found, rank otherwise.
   * Note that the rank is 1-based due to the span of zsl->header to the
   * first element. */
  //查找score和o对象在跳跃表中的排位
  unsigned long zslGetRank(zskiplist *zsl, double score, sds ele) {
      zskiplistNode *x;
      unsigned long rank = 0;
      int i;
  
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          while (x->level[i].forward &&
              (x->level[i].forward->score < score || //只要分值还小于给定的score或者
                  (x->level[i].forward->score == score &&
                  sdscmp(x->level[i].forward->ele,ele) <= 0))) {
              rank += x->level[i].span;
              x = x->level[i].forward;
          }
  
          /* x might be equal to zsl->header, so test if obj is non-NULL */
          //确保在第i层找到分值相同，且对象相同时才会返回排位值
          if (x->ele && sdscmp(x->ele,ele) == 0) {
              return rank;
          }
      }
      return 0;
  }
  
  /* Finds an element by its rank. The rank argument needs to be 1-based. */
  //返回排位为rank的节点地址
  zskiplistNode* zslGetElementByRank(zskiplist *zsl, unsigned long rank) {
      zskiplistNode *x;
      unsigned long traversed = 0; //排位值，跨越过的节点数
      int i;
  
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {//遍历头结点的每一层
          while (x->level[i].forward && (traversed + x->level[i].span) <= rank)//知道traversed还没到到达rank
          {
              traversed += x->level[i].span;
              x = x->level[i].forward;//指向下一个节点
          }
          if (traversed == rank) {
              return x;
          }
      }
      return NULL;
  }
  
  /* Populate the rangespec according to the objects min and max. */
  //设置spec中的min和max值
  static int zslParseRange(robj *min, robj *max, zrangespec *spec) {
      char *eptr;
      spec->minex = spec->maxex = 0;
  
      /* Parse the min-max interval. If one of the values is prefixed
       * by the "(" character, it's considered "open". For instance
       * ZRANGEBYSCORE zset (1.5 (2.5 will match min < x < max
       * ZRANGEBYSCORE zset 1.5 2.5 will instead match min <= x <= max */
      //处理最小值min
      if (min->encoding == OBJ_ENCODING_INT) {//如果该对象是用整数实现的
          spec->min = (long)min->ptr;//设置min值
      } else {//如果对象是用字符串实现的
          if (((char*)min->ptr)[0] == '(') {
              spec->min = strtod((char*)min->ptr+1,&eptr);//将字符串转换为double类型的值，eptr用来存储不和条件的字符串地址
              if (eptr[0] != '\0' || isnan(spec->min)) return C_ERR;
              spec->minex = 1;
          } else {
              spec->min = strtod((char*)min->ptr,&eptr);
              if (eptr[0] != '\0' || isnan(spec->min)) return C_ERR;
          }
      }
      if (max->encoding == OBJ_ENCODING_INT) { //如果该对象是用整数实现的
          spec->max = (long)max->ptr; //设置max值
      } else {
          if (((char*)max->ptr)[0] == '(') {
              spec->max = strtod((char*)max->ptr+1,&eptr); //将字符串转换为double类型的值，eptr用来存储不和条件的字符串地址
              if (eptr[0] != '\0' || isnan(spec->max)) return C_ERR;
              spec->maxex = 1;
          } else {
              spec->max = strtod((char*)max->ptr,&eptr);
              if (eptr[0] != '\0' || isnan(spec->max)) return C_ERR;
          }
      }
  
      return C_OK;
  }
  
  /* ------------------------ Lexicographic ranges ---------------------------- */
  
  /* Parse max or min argument of ZRANGEBYLEX.
    * (foo means foo (open interval)
    * [foo means foo (closed interval)
    * - means the min string possible
    * + means the max string possible
    *
    * If the string is valid the *dest pointer is set to the redis object
    * that will be used for the comparison, and ex will be set to 0 or 1
    * respectively if the item is exclusive or inclusive. C_OK will be
    * returned.
    *
    * If the string is not a valid range C_ERR is returned, and the value
    * of *dest and *ex is undefined. */
   // 解析ZRANGEBYLEX命令的最大值和最小值参数
  int zslParseLexRangeItem(robj *item, sds *dest, int *ex) {//解析字典序的对象
      char *c = item->ptr;
  
      switch(c[0]) {
      case '+'://+ 意味这值最大的字符串
          if (c[1] != '\0') return C_ERR;
          *ex = 1;
          *dest = shared.maxstring;
          return C_OK;
      case '-': //- 意味这值最小的字符串
          if (c[1] != '\0') return C_ERR;
          *ex = 1;
          *dest = shared.minstring;
          return C_OK;
      case '(': //( 意味这是左开区间
          *ex = 1;
          *dest = sdsnewlen(c+1,sdslen(c)-1);
          return C_OK;
      case '[': //[ 意味这左闭区间
          *ex = 0;
          *dest = sdsnewlen(c+1,sdslen(c)-1);
          return C_OK;
      default:
          return C_ERR;
      }
  }
  
  /* Free a lex range structure, must be called only after zelParseLexRange()
   * populated the structure with success (C_OK returned). */
  void zslFreeLexRange(zlexrangespec *spec) {
      if (spec->min != shared.minstring &&
          spec->min != shared.maxstring) sdsfree(spec->min);
      if (spec->max != shared.minstring &&
          spec->max != shared.maxstring) sdsfree(spec->max);
  }
  
  /* Populate the lex rangespec according to the objects min and max.
   *
   * Return C_OK on success. On error C_ERR is returned.
   * When OK is returned the structure must be freed with zslFreeLexRange(),
   * otherwise no release is needed. */
  //根据最大值对象和最小值对象设置
  int zslParseLexRange(robj *min, robj *max, zlexrangespec *spec) {
      /* The range can't be valid if objects are integer encoded.
       * Every item must start with ( or [. */
      // 最大值对象和最小值对象不能是整数编码，因为第一个字符是( or [. */
      if (min->encoding == OBJ_ENCODING_INT ||
          max->encoding == OBJ_ENCODING_INT) return C_ERR; 
  
      //初始化最大值和最小值
      spec->min = spec->max = NULL;
      //解析最小值和最大值，如果任意出错则释放最小值和最大值空间，返回-1
      //解析成功，则设置spec的成员
      if (zslParseLexRangeItem(min, &spec->min, &spec->minex) == C_ERR ||
          zslParseLexRangeItem(max, &spec->max, &spec->maxex) == C_ERR) {
          zslFreeLexRange(spec);
          return C_ERR;
      } else {
          return C_OK;
      }
  }
  
  /* This is just a wrapper to sdscmp() that is able to
   * handle shared.minstring and shared.maxstring as the equivalent of
   * -inf and +inf for strings */
  // 比较两个对象，能够处理shared.minstring and shared.maxstring的情况，相等返回0
  int sdscmplex(sds a, sds b) {
      if (a == b) return 0;
      if (a == shared.minstring || b == shared.maxstring) return -1;
      if (a == shared.maxstring || b == shared.minstring) return 1;
      return sdscmp(a,b);
  }
  
  // 比较value对象和规定的分数范围的最小值，返回1表示大于spec最小值
  int zslLexValueGteMin(sds value, zlexrangespec *spec) {
      return spec->minex ?
          (sdscmplex(value,spec->min) > 0) :
          (sdscmplex(value,spec->min) >= 0);
  }
  
  // 比较value对象和规定的分数范围的最大值，返回1表示小于spec最大值
  int zslLexValueLteMax(sds value, zlexrangespec *spec) {
      return spec->maxex ?
          (sdscmplex(value,spec->max) < 0) :
          (sdscmplex(value,spec->max) <= 0);
  }
  
  /* Returns if there is a part of the zset is in the lex range. */
  // 返回一个zset是否有一部分在range的范围内
  int zslIsInLexRange(zskiplist *zsl, zlexrangespec *range) {
      zskiplistNode *x;
  
      /* Test for ranges that will always be empty. */
      // 测试range的范围是否合法
      int cmp = sdscmplex(range->min,range->max);
      if (cmp > 0 || (cmp == 0 && (range->minex || range->maxex)))
          return 0;
      x = zsl->tail;
      // ！查看跳跃表的尾节点的对象是否比range的最小值还大，
      if (x == NULL || !zslLexValueGteMin(x->ele,range))
          return 0;
      x = zsl->header->level[0].forward;
      // ！查看跳跃表的头节点的对象是否比range的最大值还小，
      if (x == NULL || !zslLexValueLteMax(x->ele,range))
          return 0;
      return 1;
  }
  
  /* Find the first node that is contained in the specified lex range.
   * Returns NULL when no element is contained in the range. */
  // 返回第一个包含在range范围内的节点的地址
  zskiplistNode *zslFirstInLexRange(zskiplist *zsl, zlexrangespec *range) {
      zskiplistNode *x;
      int i;
  
      /* If everything is out of range, return early. */
      // zsl是否有一部分包含在range内，没有则返回NULL
      if (!zslIsInLexRange(zsl,range)) return NULL;
  
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          /* Go forward while *OUT* of range. */
          // 一直前进寻找，当某一个节点比range的最小值大时，停止寻找
          while (x->level[i].forward &&
              !zslLexValueGteMin(x->level[i].forward->ele,range))
                  x = x->level[i].forward;
      }
  
      /* This is an inner range, so the next node cannot be NULL. */
      x = x->level[0].forward;
      serverAssert(x != NULL);
  
      /* Check if score <= max. */
      if (!zslLexValueLteMax(x->ele,range)) return NULL;
      return x;
  }
  
  /* Find the last node that is contained in the specified range.
   * Returns NULL when no element is contained in the range. */
  // 返回最后一个包含在range范围内的节点的地址
  zskiplistNode *zslLastInLexRange(zskiplist *zsl, zlexrangespec *range) {
      zskiplistNode *x;
      int i;
  
      /* If everything is out of range, return early. */
      if (!zslIsInLexRange(zsl,range)) return NULL;
  
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          /* Go forward while *IN* range. */
          while (x->level[i].forward &&
              zslLexValueLteMax(x->level[i].forward->ele,range))
                  x = x->level[i].forward;
      }
  
      /* This is an inner range, so this node cannot be NULL. */
      serverAssert(x != NULL);
  
      /* Check if score >= min. */
      if (!zslLexValueGteMin(x->ele,range)) return NULL;
      return x;
  }
  
  /*-----------------------------------------------------------------------------
   * Ziplist-backed sorted set API
   *----------------------------------------------------------------------------*/
  // 从sptr指向的entry中取出有序集合的分值
  double zzlGetScore(unsigned char *sptr) {
      unsigned char *vstr;
      unsigned int vlen;
      long long vlong;
      char buf[128];
      double score;
  
      serverAssert(sptr != NULL);
      // 将sptr指向的entry保存到参数中
      serverAssert(ziplistGet(sptr,&vstr,&vlen,&vlong));
      // 如果是字符串类型的值
      if (vstr) {
          // 拷贝到buf中
          memcpy(buf,vstr,vlen);
          buf[vlen] = '\0';
          // 转换成double类型
          score = strtod(buf,NULL);
      } else {
          score = vlong;
      }
  
      return score;
  }
  
  /* Return a ziplist element as an SDS string. */
  // 返回一个sptr指向entry所构建的字符串类型的对象地址
  sds ziplistGetObject(unsigned char *sptr) {
      unsigned char *vstr;
      unsigned int vlen;
      long long vlong;
  
      serverAssert(sptr != NULL);
      // 将sptr指向的entry保存到参数中
      serverAssert(ziplistGet(sptr,&vstr,&vlen,&vlong));
  
      // 根据不同类型的值，创建返回字符串对象
      if (vstr) {
          return sdsnewlen((char*)vstr,vlen);
      } else {
          return sdsfromlonglong(vlong);
      }
  }
  
  /* Compare element in sorted set with given element. */
  // 比较eptr和cstr指向的元素，返回0表示相等，正整数表示eptr比cstr大
  int zzlCompareElements(unsigned char *eptr, unsigned char *cstr, unsigned int clen) {
      unsigned char *vstr;
      unsigned int vlen;
      long long vlong;
      unsigned char vbuf[32];
      int minlen, cmp;
      // 将eptr指向的entry保存到参数中
      serverAssert(ziplistGet(eptr,&vstr,&vlen,&vlong));
      if (vstr == NULL) {
          /* Store string representation of long long in buf. */
          vlen = ll2string((char*)vbuf,sizeof(vbuf),vlong);
          vstr = vbuf;
      }
  
      // 比较最小长度
      minlen = (vlen < clen) ? vlen : clen;
      cmp = memcmp(vstr,cstr,minlen);
      if (cmp == 0) return vlen-clen;//minlen长度的子串相等，返回长度差值
      return cmp;
  }
  
  // 返回有序集合的元素个数
  unsigned int zzlLength(unsigned char *zl) {
      return ziplistLen(zl)/2;
  }
  
  /* Move to next entry based on the values in eptr and sptr. Both are set to
   * NULL when there is no next entry. */
  // 将当前的元素指针eptr和当前元素分值的指针sptr都指向下一个元素和元素的分值
  void zzlNext(unsigned char *zl, unsigned char **eptr, unsigned char **sptr) {
      unsigned char *_eptr, *_sptr;
      serverAssert(*eptr != NULL && *sptr != NULL);
  
      // 下一个元素的地址为当前元素分值的下一个entry
      _eptr = ziplistNext(zl,*sptr);
      if (_eptr != NULL) {
          // 下一个元素分值的地址为下一个元素的下一个entry
          _sptr = ziplistNext(zl,_eptr);
          serverAssert(_sptr != NULL);
      } else {
          /* No next entry. */
          _sptr = NULL;
      }
  
      *eptr = _eptr;
      *sptr = _sptr;
  }
  
  /* Move to the previous entry based on the values in eptr and sptr. Both are
   * set to NULL when there is no next entry. */
  // 将当前的元素指针eptr和当前元素分值的指针sptr都指向上一个元素和元素的分值
  void zzlPrev(unsigned char *zl, unsigned char **eptr, unsigned char **sptr) {
      unsigned char *_eptr, *_sptr;
      serverAssert(*eptr != NULL && *sptr != NULL);
  
      // 上一个元素分值的地址为当前一个元素的上一个entry
      _sptr = ziplistPrev(zl,*eptr);
      if (_sptr != NULL) {
          // 上一个元素的地址为上一个元素分值的上一个entry
          _eptr = ziplistPrev(zl,_sptr);
          serverAssert(_eptr != NULL);
      } else {
          /* No previous entry. */
          _eptr = NULL;
      }
  
      *eptr = _eptr;
      *sptr = _sptr;
  }
  
  /* Returns if there is a part of the zset is in range. Should only be used
   * internally by zzlFirstInRange and zzlLastInRange. */
  // 判断ziplist中是否有entry节点在range范围之内，有一个则返回1，否则返回0
  int zzlIsInRange(unsigned char *zl, zrangespec *range) {
      unsigned char *p;
      double score;
  
      /* Test for ranges that will always be empty. */
      // 测试range是否合法
      if (range->min > range->max ||
              (range->min == range->max && (range->minex || range->maxex)))
          return 0;
  
      // 保存ziplist总最后一个entry节点的地址，保存着有序集合的最大分值
      p = ziplistIndex(zl,-1); /* Last score. */
      if (p == NULL) return 0; /* Empty sorted set */
      // 取出有序集合的最大分值
      score = zzlGetScore(p);
      // 如果最大分值比range的最小最小，返回0
      if (!zslValueGteMin(score,range))
          return 0;
  
      // 保存ziplist总第一个entry节点的地址，保存着有序集合的最小分值
      p = ziplistIndex(zl,1); /* First score. */
      serverAssert(p != NULL);
      // 取出有序集合的最小分值
      score = zzlGetScore(p);
      // 如果最小分值比range的最大最大，返回0
      if (!zslValueLteMax(score,range))
          return 0;
  
      return 1;
  }
  
  /* Find pointer to the first element contained in the specified range.
   * Returns NULL when no element is contained in the range. */
  // 返回第一个满足range范围的entry节点的地址
  unsigned char *zzlFirstInRange(unsigned char *zl, zrangespec *range) {
      unsigned char *eptr = ziplistIndex(zl,0), *sptr;
      double score;
  
      /* If everything is out of range, return early. */
      // 先判断是否至少有一个entry符合range，没有返回NULL
      if (!zzlIsInRange(zl,range)) return NULL;
  
      // 遍历ziplist的所有entry
      while (eptr != NULL) {
          // 保存当前元素分值的entry地址
          sptr = ziplistNext(zl,eptr);
          serverAssert(sptr != NULL);
  
          // 取出当前元素的分值
          score = zzlGetScore(sptr);
          // 如果分值大于range的最小值
          if (zslValueGteMin(score,range)) {
              /* Check if score <= max. */
              if (zslValueLteMax(score,range))
                  return eptr;
              return NULL;
          }
  
          /* Move to next element. */
          eptr = ziplistNext(zl,sptr);
      }
  
      return NULL;
  }
  
  /* Find pointer to the last element contained in the specified range.
   * Returns NULL when no element is contained in the range. */
  // 返回最后一个满足range范围的entry节点的地址
  unsigned char *zzlLastInRange(unsigned char *zl, zrangespec *range) {
      unsigned char *eptr = ziplistIndex(zl,-2), *sptr;
      double score;
  
      /* If everything is out of range, return early. */
      if (!zzlIsInRange(zl,range)) return NULL;
  
      // 遍历ziplist的所有entry
      while (eptr != NULL) {
          // 保存当前元素分值的entry地址
          sptr = ziplistNext(zl,eptr);
          serverAssert(sptr != NULL);
          // 取出当前元素的分值
          score = zzlGetScore(sptr);
          // 如果分值小于range的最大值
          if (zslValueLteMax(score,range)) {
              /* Check if score >= min. */
              // 分值还大于range的最小值
              if (zslValueGteMin(score,range))
                  // 返回当前节点的地址
                  return eptr;
              return NULL;
          }
  
          /* Move to previous element by moving to the score of previous element.
           * When this returns NULL, we know there also is no element. */
          // 指向前一个元素和元素的分值
          sptr = ziplistPrev(zl,eptr);
          if (sptr != NULL)
              serverAssert((eptr = ziplistPrev(zl,sptr)) != NULL);
          else
              eptr = NULL;
      }
  
      return NULL;
  }
  
  // 比较p指向的entry的值和规定范围spec，返回1表示大于spec的最大值
  int zzlLexValueGteMin(unsigned char *p, zlexrangespec *spec) {
      sds value = ziplistGetObject(p);
      int res = zslLexValueGteMin(value,spec);
      sdsfree(value);
      return res;
  }
  
  // 比较p指向的entry的值和规定范围spec，返回1表示小于spec的最小值
  int zzlLexValueLteMax(unsigned char *p, zlexrangespec *spec) {
      sds value = ziplistGetObject(p);
      int res = zslLexValueLteMax(value,spec);
      sdsfree(value);
      return res;
  }
  
  /* Returns if there is a part of the zset is in range. Should only be used
   * internally by zzlFirstInRange and zzlLastInRange. */
  // 判断ziplist中是否有entry节点在range范围之内，有一个则返回1，否则返回0
  int zzlIsInLexRange(unsigned char *zl, zlexrangespec *range) {
      unsigned char *p;
  
      /* Test for ranges that will always be empty. */
      // 测试字典序范围是否合法
      int cmp = sdscmplex(range->min,range->max);
      if (cmp > 0 || (cmp == 0 && (range->minex || range->maxex)))
          return 0;
  
      // 最后一个元素的地址
      p = ziplistIndex(zl,-2); /* Last element. */
      if (p == NULL) return 0;
      // 小于range的最小值，返回0
      if (!zzlLexValueGteMin(p,range))
          return 0;
  
      // 第一个元素地址
      p = ziplistIndex(zl,0); /* First element. */
      serverAssert(p != NULL);
      // 大于range的最大值，返回0
      if (!zzlLexValueLteMax(p,range))
          return 0;
  
      return 1;
  }
  
  /* Find pointer to the first element contained in the specified lex range.
   * Returns NULL when no element is contained in the range. */
  // 返回第一个满足range范围的元素的地址
  unsigned char *zzlFirstInLexRange(unsigned char *zl, zlexrangespec *range) {
      //第一个元素节点地址，从前往后遍历
      unsigned char *eptr = ziplistIndex(zl,0), *sptr;
  
      /* If everything is out of range, return early. */
      // 判断ziplist中是否有entry节点在range范围之内，有一个则返回1，否则返回0
      if (!zzlIsInLexRange(zl,range)) return NULL;
  
      // 遍历所有元素节点
      while (eptr != NULL) {
          // 大于最小值且小于最大值，返回当前节点地址
          if (zzlLexValueGteMin(eptr,range)) {
              /* Check if score <= max. */
              if (zzlLexValueLteMax(eptr,range))
                  return eptr;
              return NULL;
          }
  
          /* Move to next element. */
          //跳过分值节点
          sptr = ziplistNext(zl,eptr); /* This element score. Skip it. */
          serverAssert(sptr != NULL);
          // 指向下一个元素节点
          eptr = ziplistNext(zl,sptr); /* Next element. */
      }
  
      return NULL;
  }
  
  /* Find pointer to the last element contained in the specified lex range.
   * Returns NULL when no element is contained in the range. */
  // 返回最后一个满足range范围的元素的地址
  unsigned char *zzlLastInLexRange(unsigned char *zl, zlexrangespec *range) {
      unsigned char *eptr = ziplistIndex(zl,-2), *sptr; //最后一个元素节点地址，从后往前遍历
  
      /* If everything is out of range, return early. */
      // 判断ziplist中是否有entry节点在range范围之内，有一个则返回1，否则返回0
      if (!zzlIsInLexRange(zl,range)) return NULL;
  
      // 遍历所有元素节点
      while (eptr != NULL) {
          if (zzlLexValueLteMax(eptr,range)) {
              /* Check if score >= min. */
              if (zzlLexValueGteMin(eptr,range))
                  return eptr;
              return NULL;
          }
  
          /* Move to previous element by moving to the score of previous element.
           * When this returns NULL, we know there also is no element. */
          // eptr指向前一个元素节点
          sptr = ziplistPrev(zl,eptr);
          if (sptr != NULL)
              serverAssert((eptr = ziplistPrev(zl,sptr)) != NULL);
          else
              eptr = NULL;
      }
  
      return NULL;
  }
  
  // 从ziplist中查找ele，将分值保存在score中
  unsigned char *zzlFind(unsigned char *zl, sds ele, double *score) {
      unsigned char *eptr = ziplistIndex(zl,0), *sptr; //第一个元素节点地址，从前往后遍历
  
      //得到字符串类型的ele对象
      while (eptr != NULL) {
          // 指向元素分值节点的地址
          sptr = ziplistNext(zl,eptr);
          serverAssert(sptr != NULL);
  
          if (ziplistCompare(eptr,(unsigned char*)ele,sdslen(ele))) {
              /* Matching element, pull out score. */
              if (score != NULL) *score = zzlGetScore(sptr);
              return eptr;
          }
  
          /* Move to next element. */
          eptr = ziplistNext(zl,sptr);
      }
      return NULL;
  }
  
  /* Delete (element,score) pair from ziplist. Use local copy of eptr because we
   * don't want to modify the one given as argument. */
  // 删除eptr制定的元素和分值从ziplist中
  unsigned char *zzlDelete(unsigned char *zl, unsigned char *eptr) {
      unsigned char *p = eptr;
  
      /* TODO: add function to ziplist API to delete N elements from offset. */
      // 删除元素和分值
      zl = ziplistDelete(zl,&p);
      zl = ziplistDelete(zl,&p);
      return zl;
  }
  
  //将ele元素和分值score插入到eptr指向节点的前面
  unsigned char *zzlInsertAt(unsigned char *zl, unsigned char *eptr, sds ele, double score) {
      unsigned char *sptr;
      char scorebuf[128];
      int scorelen;
      size_t offset;
  
      // 讲score转换为字符串，保存到scorebuf中，并计算score的字节长度
      scorelen = d2string(scorebuf,sizeof(scorebuf),score);
      // 如果eptr为空，则加到ziplist的尾部
      if (eptr == NULL) {
          zl = ziplistPush(zl,(unsigned char*)ele,sdslen(ele),ZIPLIST_TAIL); //添加元素节点
          zl = ziplistPush(zl,(unsigned char*)scorebuf,scorelen,ZIPLIST_TAIL); //添加分值
      } 
      // 插入在eptr节点的前面
      else {
          /* Keep offset relative to zl, as it might be re-allocated. */
          // 备份当eptr指向节点的偏移量，防止内存被重新分配
          offset = eptr-zl;
          zl = ziplistInsert(zl,eptr,(unsigned char*)ele,sdslen(ele));
          eptr = zl+offset;
  
          /* Insert score after the element. */
          serverAssert((sptr = ziplistNext(zl,eptr)) != NULL);
          zl = ziplistInsert(zl,sptr,(unsigned char*)scorebuf,scorelen);
      }
      return zl;
  }
  
  /* Insert (element,score) pair in ziplist. This function assumes the element is
   * not yet present in the list. */
  //将ele元素和分值score插入在ziplist中，从小到大排序
  unsigned char *zzlInsert(unsigned char *zl, sds ele, double score) {
      unsigned char *eptr = ziplistIndex(zl,0), *sptr; //第一个元素节点地址，从前往后遍历
      double s;
  
      while (eptr != NULL) {
          sptr = ziplistNext(zl,eptr);
          serverAssert(sptr != NULL);
          s = zzlGetScore(sptr);
  
          if (s > score) {
              /* First element with score larger than score for element to be
               * inserted. This means we should take its spot in the list to
               * maintain ordering. */
              zl = zzlInsertAt(zl,eptr,ele,score);
              break;
          } else if (s == score) {
              /* Ensure lexicographical ordering for elements. */
              if (zzlCompareElements(eptr,(unsigned char*)ele,sdslen(ele)) > 0) {
                  zl = zzlInsertAt(zl,eptr,ele,score);
                  break;
              }
          }
  
          /* Move to next element. */
          eptr = ziplistNext(zl,sptr);
      }
  
      /* Push on tail of list when it was not yet inserted. */
      if (eptr == NULL)
          zl = zzlInsertAt(zl,NULL,ele,score);
      return zl;
  }
  
  // 删除ziplist中分值在制定范围内的元素，并保存删除的数量在deleted中
  unsigned char *zzlDeleteRangeByScore(unsigned char *zl, zrangespec *range, unsigned long *deleted) {
      unsigned char *eptr, *sptr;
      double score;
      unsigned long num = 0;
  
      if (deleted != NULL) *deleted = 0;
  
      // 指向第一个符合range范围的节点
      eptr = zzlFirstInRange(zl,range);
      if (eptr == NULL) return zl;
  
      /* When the tail of the ziplist is deleted, eptr will point to the sentinel
       * byte and ziplistNext will return NULL. */
      // 循环删除节点
      while ((sptr = ziplistNext(zl,eptr)) != NULL) {
          score = zzlGetScore(sptr); //得到当前元素的分值
          // 如果元素分值在range范围内，则删除元素和分值
          if (zslValueLteMax(score,range)) {
              /* Delete both the element and the score. */
              zl = ziplistDelete(zl,&eptr);
              zl = ziplistDelete(zl,&eptr);
              //计数删除的节点个数
              num++;
          } else {
              /* No longer in range. */
              break;
          }
      }
  
      if (deleted != NULL) *deleted = num;
      return zl;
  }
  
  // 删除ziplist中分值在制定字典序范围内的元素，并保存删除的数量在deleted中
  unsigned char *zzlDeleteRangeByLex(unsigned char *zl, zlexrangespec *range, unsigned long *deleted) {
      unsigned char *eptr, *sptr;
      unsigned long num = 0;
  
      if (deleted != NULL) *deleted = 0; //初始化
  
      // 指向第一个符合range范围的元素节点
      eptr = zzlFirstInLexRange(zl,range);
      if (eptr == NULL) return zl;
  
      /* When the tail of the ziplist is deleted, eptr will point to the sentinel
       * byte and ziplistNext will return NULL. */
      // 循环删除节点
      while ((sptr = ziplistNext(zl,eptr)) != NULL) {
          // 如果元素在range范围内，则删除元素和分值
          if (zzlLexValueLteMax(eptr,range)) {
              /* Delete both the element and the score. */
              zl = ziplistDelete(zl,&eptr);
              zl = ziplistDelete(zl,&eptr);
              num++; //计数删除的节点个数
          } else {
              /* No longer in range. */
              break;
          }
      }
  
      if (deleted != NULL) *deleted = num;
      return zl;
  }
  
  /* Delete all the elements with rank between start and end from the skiplist.
   * Start and end are inclusive. Note that start and end need to be 1-based */
  // 删除给定下标范围内的所有元素
  unsigned char *zzlDeleteRangeByRank(unsigned char *zl, unsigned int start, unsigned int end, unsigned long *deleted) {
      unsigned int num = (end-start)+1;
      if (deleted) *deleted = num;
      zl = ziplistDeleteRange(zl,2*(start-1),2*num);
      return zl;
  }
  
  /*-----------------------------------------------------------------------------
   * Common sorted set API
   *----------------------------------------------------------------------------*/
  // 返回有序集合的元素个数
  unsigned long zsetLength(const robj *zobj) {
      unsigned long length = 0;
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          length = zzlLength(zobj->ptr);
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          length = ((const zset*)zobj->ptr)->zsl->length;
      } else {
          serverPanic("Unknown sorted set encoding");
      }
      return length;
  }
  
  // 将有序集合对象的编码转换为encoding制定的编码类型
  void zsetConvert(robj *zobj, int encoding) {
      zset *zs;
      zskiplistNode *node, *next;
      sds ele;
      double score;
  
      if (zobj->encoding == encoding) return;
      // 从ziplist转换到skiplist
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
          unsigned char *vstr;
          unsigned int vlen;
          long long vlong;
  
          if (encoding != OBJ_ENCODING_SKIPLIST)
              serverPanic("Unknown target encoding");
  
          // 分配有序集合空间
          zs = zmalloc(sizeof(*zs));
          // 初始化字典和跳跃表成员
          zs->dict = dictCreate(&zsetDictType,NULL);
          zs->zsl = zslCreate();
  
          // 压缩列表的首元素指针
          eptr = ziplistIndex(zl,0);
          serverAssertWithInfo(NULL,zobj,eptr != NULL);
          // 压缩列表的首元素分值指针
          sptr = ziplistNext(zl,eptr);
          serverAssertWithInfo(NULL,zobj,sptr != NULL);
  
          // 遍历压缩列表的entry
          while (eptr != NULL) {
              score = zzlGetScore(sptr);//取出分值
              serverAssertWithInfo(NULL,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
              // 根据字符串或整数创建字符串类型对象
              if (vstr == NULL)
                  ele = sdsfromlonglong(vlong);
              else
                  ele = sdsnewlen((char*)vstr,vlen);
  
              // 将分值和成员插入到跳跃表中
              node = zslInsert(zs->zsl,score,ele);
              // 将分值和成员添加到字典中
              serverAssert(dictAdd(zs->dict,ele,&node->score) == DICT_OK);
              zzlNext(zl,&eptr,&sptr); //更新元素和分值的指针
          }
          // 转换到skiplist编码后，将原来ziplist的空间释放
          zfree(zobj->ptr);
          zobj->ptr = zs;
          zobj->encoding = OBJ_ENCODING_SKIPLIST;
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          unsigned char *zl = ziplistNew();//创建新的压缩列表
  
          if (encoding != OBJ_ENCODING_ZIPLIST)
              serverPanic("Unknown target encoding");
  
          /* Approach similar to zslFree(), since we want to free the skiplist at
           * the same time as creating the ziplist. */
          zs = zobj->ptr;
          dictRelease(zs->dict); //释放有序集合的字典，根据跳跃表遍历即可
          // 指向跳跃表的首节点
          node = zs->zsl->header->level[0].forward;
          // 释放表头节点和表头空间
          zfree(zs->zsl->header);
          zfree(zs->zsl);
  
          while (node) {
              // 将当前元素和分值尾插到列表中
              zl = zzlInsertAt(zl,NULL,node->ele,node->score);
              // 备份下一个节点地址
              next = node->level[0].forward;
              zslFreeNode(node);
              node = next;
          }
  
          zfree(zs);
          zobj->ptr = zl;
          zobj->encoding = OBJ_ENCODING_ZIPLIST;
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  }
  
  /* Convert the sorted set object into a ziplist if it is not already a ziplist
   * and if the number of elements and the maximum element size is within the
   * expected ranges. */
  // 按需转换编码成OBJ_ENCODING_ZIPLIST
  void zsetConvertToZiplistIfNeeded(robj *zobj, size_t maxelelen) {
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) return;
      zset *zset = zobj->ptr;
  
      //zset_max_ziplist_entries默认为128，表示最ziplist中最多entry的数量
      // zset_max_ziplist_value默认为64，表示ziplist一个entry的value最多为64字节
      if (zset->zsl->length <= server.zset_max_ziplist_entries &&
          maxelelen <= server.zset_max_ziplist_value)
              zsetConvert(zobj,OBJ_ENCODING_ZIPLIST);
  }
  
  /* Return (by reference) the score of the specified member of the sorted set
   * storing it into *score. If the element does not exist C_ERR is returned
   * otherwise C_OK is returned and *score is correctly populated.
   * If 'zobj' or 'member' is NULL, C_ERR is returned. */
  // 将有序集合的member成员的分值保存到score中
  int zsetScore(robj *zobj, sds member, double *score) {
      if (!zobj || !member) return C_ERR;
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          if (zzlFind(zobj->ptr, member, score) == NULL) return C_ERR;
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          dictEntry *de = dictFind(zs->dict, member);
          if (de == NULL) return C_ERR;
          *score = *(double*)dictGetVal(de);
      } else {
          serverPanic("Unknown sorted set encoding");
      }
      return C_OK;
  }
  
  /* Add a new element or update the score of an existing element in a sorted
   * set, regardless of its encoding.
   *
   * The set of flags change the command behavior. They are passed with an integer
   * pointer since the function will clear the flags and populate them with
   * other flags to indicate different conditions.
   *
   * The input flags are the following:
   *
   * ZADD_INCR: Increment the current element score by 'score' instead of updating
   *            the current element score. If the element does not exist, we
   *            assume 0 as previous score.
   * ZADD_NX:   Perform the operation only if the element does not exist.
   * ZADD_XX:   Perform the operation only if the element already exist.
   *
   * When ZADD_INCR is used, the new score of the element is stored in
   * '*newscore' if 'newscore' is not NULL.
   *
   * The returned flags are the following:
   *
   * ZADD_NAN:     The resulting score is not a number.
   * ZADD_ADDED:   The element was added (not present before the call).
   * ZADD_UPDATED: The element score was updated.
   * ZADD_NOP:     No operation was performed because of NX or XX.
   *
   * Return value:
   *
   * The function returns 1 on success, and sets the appropriate flags
   * ADDED or UPDATED to signal what happened during the operation (note that
   * none could be set if we re-added an element using the same score it used
   * to have, or in the case a zero increment is used).
   *
   * The function returns 0 on error, currently only when the increment
   * produces a NAN condition, or when the 'score' value is NAN since the
   * start.
   *
   * The command as a side effect of adding a new element may convert the sorted
   * set internal encoding from ziplist to hashtable+skiplist.
   *
   * Memory management of 'ele':
   *
   * The function does not take ownership of the 'ele' SDS string, but copies
   * it if needed. */
  int zsetAdd(robj *zobj, double score, sds ele, int *flags, double *newscore) {
      /* Turn options into simple to check vars. */
      int incr = (*flags & ZADD_INCR) != 0;
      int nx = (*flags & ZADD_NX) != 0;
      int xx = (*flags & ZADD_XX) != 0;
      *flags = 0; /* We'll return our response flags. */
      double curscore;
  
      /* NaN as input is an error regardless of all the other parameters. */
      if (isnan(score)) {
          *flags = ZADD_NAN;
          return 0;
      }
  
      /* Update the sorted set according to its encoding. */
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *eptr;
  
          if ((eptr = zzlFind(zobj->ptr,ele,&curscore)) != NULL) {
              /* NX? Return, same element already exists. */
              if (nx) {
                  *flags |= ZADD_NOP;
                  return 1;
              }
  
              /* Prepare the score for the increment if needed. */
              if (incr) {
                  score += curscore;
                  if (isnan(score)) {
                      *flags |= ZADD_NAN;
                      return 0;
                  }
                  if (newscore) *newscore = score;
              }
  
              /* Remove and re-insert when score changed. */
              if (score != curscore) {
                  zobj->ptr = zzlDelete(zobj->ptr,eptr);
                  zobj->ptr = zzlInsert(zobj->ptr,ele,score);
                  *flags |= ZADD_UPDATED;
              }
              return 1;
          } else if (!xx) {
              /* Optimize: check if the element is too large or the list
               * becomes too long *before* executing zzlInsert. */
              zobj->ptr = zzlInsert(zobj->ptr,ele,score);
              if (zzlLength(zobj->ptr) > server.zset_max_ziplist_entries ||
                  sdslen(ele) > server.zset_max_ziplist_value)
                  zsetConvert(zobj,OBJ_ENCODING_SKIPLIST);
              if (newscore) *newscore = score;
              *flags |= ZADD_ADDED;
              return 1;
          } else {
              *flags |= ZADD_NOP;
              return 1;
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplistNode *znode;
          dictEntry *de;
  
          de = dictFind(zs->dict,ele);
          if (de != NULL) {
              /* NX? Return, same element already exists. */
              if (nx) {
                  *flags |= ZADD_NOP;
                  return 1;
              }
              curscore = *(double*)dictGetVal(de);
  
              /* Prepare the score for the increment if needed. */
              if (incr) {
                  score += curscore;
                  if (isnan(score)) {
                      *flags |= ZADD_NAN;
                      return 0;
                  }
                  if (newscore) *newscore = score;
              }
  
              /* Remove and re-insert when score changes. */
              if (score != curscore) {
                  znode = zslUpdateScore(zs->zsl,curscore,ele,score);
                  /* Note that we did not removed the original element from
                   * the hash table representing the sorted set, so we just
                   * update the score. */
                  dictGetVal(de) = &znode->score; /* Update score ptr. */
                  *flags |= ZADD_UPDATED;
              }
              return 1;
          } else if (!xx) {
              ele = sdsdup(ele);
              znode = zslInsert(zs->zsl,score,ele);
              serverAssert(dictAdd(zs->dict,ele,&znode->score) == DICT_OK);
              *flags |= ZADD_ADDED;
              if (newscore) *newscore = score;
              return 1;
          } else {
              *flags |= ZADD_NOP;
              return 1;
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
      return 0; /* Never reached. */
  }
  
  /* Delete the element 'ele' from the sorted set, returning 1 if the element
   * existed and was deleted, 0 otherwise (the element was not there). */
  int zsetDel(robj *zobj, sds ele) {
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *eptr;
  
          if ((eptr = zzlFind(zobj->ptr,ele,NULL)) != NULL) {
              zobj->ptr = zzlDelete(zobj->ptr,eptr);
              return 1;
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          dictEntry *de;
          double score;
  
          de = dictUnlink(zs->dict,ele);
          if (de != NULL) {
              /* Get the score in order to delete from the skiplist later. */
              score = *(double*)dictGetVal(de);
  
              /* Delete from the hash table and later from the skiplist.
               * Note that the order is important: deleting from the skiplist
               * actually releases the SDS string representing the element,
               * which is shared between the skiplist and the hash table, so
               * we need to delete from the skiplist as the final step. */
              dictFreeUnlinkedEntry(zs->dict,de);
  
              /* Delete from skiplist. */
              int retval = zslDelete(zs->zsl,score,ele,NULL);
              serverAssert(retval);
  
              if (htNeedsResize(zs->dict)) dictResize(zs->dict);
              return 1;
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
      return 0; /* No such element found. */
  }
  
  /* Given a sorted set object returns the 0-based rank of the object or
   * -1 if the object does not exist.
   *
   * For rank we mean the position of the element in the sorted collection
   * of elements. So the first element has rank 0, the second rank 1, and so
   * forth up to length-1 elements.
   *
   * If 'reverse' is false, the rank is returned considering as first element
   * the one with the lowest score. Otherwise if 'reverse' is non-zero
   * the rank is computed considering as element with rank 0 the one with
   * the highest score. */
  long zsetRank(robj *zobj, sds ele, int reverse) {
      unsigned long llen;
      unsigned long rank;
  
      llen = zsetLength(zobj);
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
  
          eptr = ziplistIndex(zl,0);
          serverAssert(eptr != NULL);
          sptr = ziplistNext(zl,eptr);
          serverAssert(sptr != NULL);
  
          rank = 1;
          while(eptr != NULL) {
              if (ziplistCompare(eptr,(unsigned char*)ele,sdslen(ele)))
                  break;
              rank++;
              zzlNext(zl,&eptr,&sptr);
          }
  
          if (eptr != NULL) {
              if (reverse)
                  return llen-rank;
              else
                  return rank-1;
          } else {
              return -1;
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          dictEntry *de;
          double score;
  
          de = dictFind(zs->dict,ele);
          if (de != NULL) {
              score = *(double*)dictGetVal(de);
              rank = zslGetRank(zsl,score,ele);
              /* Existing elements always have a rank. */
              serverAssert(rank != 0);
              if (reverse)
                  return llen-rank;
              else
                  return rank-1;
          } else {
              return -1;
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  }
  
  /*-----------------------------------------------------------------------------
   * Sorted set commands
   *----------------------------------------------------------------------------*/
  
  /* This generic command implements both ZADD and ZINCRBY. */
  void zaddGenericCommand(client *c, int flags) {
      static char *nanerr = "resulting score is not a number (NaN)";
      robj *key = c->argv[1];
      robj *zobj;
      sds ele;
      double score = 0, *scores = NULL;
      int j, elements;
      int scoreidx = 0;
      /* The following vars are used in order to track what the command actually
       * did during the execution, to reply to the client and to trigger the
       * notification of keyspace change. */
      int added = 0;      /* Number of new elements added. */
      int updated = 0;    /* Number of elements with updated score. */
      int processed = 0;  /* Number of elements processed, may remain zero with
                             options like XX. */
  
      /* Parse options. At the end 'scoreidx' is set to the argument position
       * of the score of the first score-element pair. */
      scoreidx = 2;
      while(scoreidx < c->argc) {
          char *opt = c->argv[scoreidx]->ptr;
          if (!strcasecmp(opt,"nx")) flags |= ZADD_NX;
          else if (!strcasecmp(opt,"xx")) flags |= ZADD_XX;
          else if (!strcasecmp(opt,"ch")) flags |= ZADD_CH;
          else if (!strcasecmp(opt,"incr")) flags |= ZADD_INCR;
          else break;
          scoreidx++;
      }
  
      /* Turn options into simple to check vars. */
      int incr = (flags & ZADD_INCR) != 0;
      int nx = (flags & ZADD_NX) != 0;
      int xx = (flags & ZADD_XX) != 0;
      int ch = (flags & ZADD_CH) != 0;
  
      /* After the options, we expect to have an even number of args, since
       * we expect any number of score-element pairs. */
      elements = c->argc-scoreidx;
      if (elements % 2 || !elements) {
          addReply(c,shared.syntaxerr);
          return;
      }
      elements /= 2; /* Now this holds the number of score-element pairs. */
  
      /* Check for incompatible options. */
      if (nx && xx) {
          addReplyError(c,
              "XX and NX options at the same time are not compatible");
          return;
      }
  
      if (incr && elements > 1) {
          addReplyError(c,
              "INCR option supports a single increment-element pair");
          return;
      }
  
      /* Start parsing all the scores, we need to emit any syntax error
       * before executing additions to the sorted set, as the command should
       * either execute fully or nothing at all. */
      scores = zmalloc(sizeof(double)*elements);
      for (j = 0; j < elements; j++) {
          if (getDoubleFromObjectOrReply(c,c->argv[scoreidx+j*2],&scores[j],NULL)
              != C_OK) goto cleanup;
      }
  
      /* Lookup the key and create the sorted set if does not exist. */
      zobj = lookupKeyWrite(c->db,key);
      if (zobj == NULL) {
          if (xx) goto reply_to_client; /* No key + XX option: nothing to do. */
          if (server.zset_max_ziplist_entries == 0 ||
              server.zset_max_ziplist_value < sdslen(c->argv[scoreidx+1]->ptr))
          {
              zobj = createZsetObject();
          } else {
              zobj = createZsetZiplistObject();
          }
          dbAdd(c->db,key,zobj);
      } else {
          if (zobj->type != OBJ_ZSET) {
              addReply(c,shared.wrongtypeerr);
              goto cleanup;
          }
      }
  
      for (j = 0; j < elements; j++) {
          double newscore;
          score = scores[j];
          int retflags = flags;
  
          ele = c->argv[scoreidx+1+j*2]->ptr;
          int retval = zsetAdd(zobj, score, ele, &retflags, &newscore);
          if (retval == 0) {
              addReplyError(c,nanerr);
              goto cleanup;
          }
          if (retflags & ZADD_ADDED) added++;
          if (retflags & ZADD_UPDATED) updated++;
          if (!(retflags & ZADD_NOP)) processed++;
          score = newscore;
      }
      server.dirty += (added+updated);
  
  reply_to_client:
      if (incr) { /* ZINCRBY or INCR option. */
          if (processed)
              addReplyDouble(c,score);
          else
              addReplyNull(c);
      } else { /* ZADD. */
          addReplyLongLong(c,ch ? added+updated : added);
      }
  
  cleanup:
      zfree(scores);
      if (added || updated) {
          signalModifiedKey(c,c->db,key);
          notifyKeyspaceEvent(NOTIFY_ZSET,
              incr ? "zincr" : "zadd", key, c->db->id);
      }
  }
  
  void zaddCommand(client *c) {
      zaddGenericCommand(c,ZADD_NONE);
  }
  
  void zincrbyCommand(client *c) {
      zaddGenericCommand(c,ZADD_INCR);
  }
  
  void zremCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
      int deleted = 0, keyremoved = 0, j;
  
      if ((zobj = lookupKeyWriteOrReply(c,key,shared.czero)) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      for (j = 2; j < c->argc; j++) {
          if (zsetDel(zobj,c->argv[j]->ptr)) deleted++;
          if (zsetLength(zobj) == 0) {
              dbDelete(c->db,key);
              keyremoved = 1;
              break;
          }
      }
  
      if (deleted) {
          notifyKeyspaceEvent(NOTIFY_ZSET,"zrem",key,c->db->id);
          if (keyremoved)
              notifyKeyspaceEvent(NOTIFY_GENERIC,"del",key,c->db->id);
          signalModifiedKey(c,c->db,key);
          server.dirty += deleted;
      }
      addReplyLongLong(c,deleted);
  }
  
  /* Implements ZREMRANGEBYRANK, ZREMRANGEBYSCORE, ZREMRANGEBYLEX commands. */
  #define ZRANGE_RANK 0
  #define ZRANGE_SCORE 1
  #define ZRANGE_LEX 2
  void zremrangeGenericCommand(client *c, int rangetype) {
      robj *key = c->argv[1];
      robj *zobj;
      int keyremoved = 0;
      unsigned long deleted = 0;
      zrangespec range;
      zlexrangespec lexrange;
      long start, end, llen;
  
      /* Step 1: Parse the range. */
      if (rangetype == ZRANGE_RANK) {
          if ((getLongFromObjectOrReply(c,c->argv[2],&start,NULL) != C_OK) ||
              (getLongFromObjectOrReply(c,c->argv[3],&end,NULL) != C_OK))
              return;
      } else if (rangetype == ZRANGE_SCORE) {
          if (zslParseRange(c->argv[2],c->argv[3],&range) != C_OK) {
              addReplyError(c,"min or max is not a float");
              return;
          }
      } else if (rangetype == ZRANGE_LEX) {
          if (zslParseLexRange(c->argv[2],c->argv[3],&lexrange) != C_OK) {
              addReplyError(c,"min or max not valid string range item");
              return;
          }
      }
  
      /* Step 2: Lookup & range sanity checks if needed. */
      if ((zobj = lookupKeyWriteOrReply(c,key,shared.czero)) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) goto cleanup;
  
      if (rangetype == ZRANGE_RANK) {
          /* Sanitize indexes. */
          llen = zsetLength(zobj);
          if (start < 0) start = llen+start;
          if (end < 0) end = llen+end;
          if (start < 0) start = 0;
  
          /* Invariant: start >= 0, so this test will be true when end < 0.
           * The range is empty when start > end or start >= length. */
          if (start > end || start >= llen) {
              addReply(c,shared.czero);
              goto cleanup;
          }
          if (end >= llen) end = llen-1;
      }
  
      /* Step 3: Perform the range deletion operation. */
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          switch(rangetype) {
          case ZRANGE_RANK:
              zobj->ptr = zzlDeleteRangeByRank(zobj->ptr,start+1,end+1,&deleted);
              break;
          case ZRANGE_SCORE:
              zobj->ptr = zzlDeleteRangeByScore(zobj->ptr,&range,&deleted);
              break;
          case ZRANGE_LEX:
              zobj->ptr = zzlDeleteRangeByLex(zobj->ptr,&lexrange,&deleted);
              break;
          }
          if (zzlLength(zobj->ptr) == 0) {
              dbDelete(c->db,key);
              keyremoved = 1;
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          switch(rangetype) {
          case ZRANGE_RANK:
              deleted = zslDeleteRangeByRank(zs->zsl,start+1,end+1,zs->dict);
              break;
          case ZRANGE_SCORE:
              deleted = zslDeleteRangeByScore(zs->zsl,&range,zs->dict);
              break;
          case ZRANGE_LEX:
              deleted = zslDeleteRangeByLex(zs->zsl,&lexrange,zs->dict);
              break;
          }
          if (htNeedsResize(zs->dict)) dictResize(zs->dict);
          if (dictSize(zs->dict) == 0) {
              dbDelete(c->db,key);
              keyremoved = 1;
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      /* Step 4: Notifications and reply. */
      if (deleted) {
          char *event[3] = {"zremrangebyrank","zremrangebyscore","zremrangebylex"};
          signalModifiedKey(c,c->db,key);
          notifyKeyspaceEvent(NOTIFY_ZSET,event[rangetype],key,c->db->id);
          if (keyremoved)
              notifyKeyspaceEvent(NOTIFY_GENERIC,"del",key,c->db->id);
      }
      server.dirty += deleted;
      addReplyLongLong(c,deleted);
  
  cleanup:
      if (rangetype == ZRANGE_LEX) zslFreeLexRange(&lexrange);
  }
  
  void zremrangebyrankCommand(client *c) {
      zremrangeGenericCommand(c,ZRANGE_RANK);
  }
  
  void zremrangebyscoreCommand(client *c) {
      zremrangeGenericCommand(c,ZRANGE_SCORE);
  }
  
  void zremrangebylexCommand(client *c) {
      zremrangeGenericCommand(c,ZRANGE_LEX);
  }
  
  typedef struct {
      robj *subject;
      int type; /* Set, sorted set */
      int encoding;
      double weight;
  
      union {
          /* Set iterators. */
          union _iterset {
              struct {
                  intset *is;
                  int ii;
              } is;
              struct {
                  dict *dict;
                  dictIterator *di;
                  dictEntry *de;
              } ht;
          } set;
  
          /* Sorted set iterators. */
          union _iterzset {
              struct {
                  unsigned char *zl;
                  unsigned char *eptr, *sptr;
              } zl;
              struct {
                  zset *zs;
                  zskiplistNode *node;
              } sl;
          } zset;
      } iter;
  } zsetopsrc;
  
  
  /* Use dirty flags for pointers that need to be cleaned up in the next
   * iteration over the zsetopval. The dirty flag for the long long value is
   * special, since long long values don't need cleanup. Instead, it means that
   * we already checked that "ell" holds a long long, or tried to convert another
   * representation into a long long value. When this was successful,
   * OPVAL_VALID_LL is set as well. */
  #define OPVAL_DIRTY_SDS 1
  #define OPVAL_DIRTY_LL 2
  #define OPVAL_VALID_LL 4
  
  /* Store value retrieved from the iterator. */
  typedef struct {
      int flags;
      unsigned char _buf[32]; /* Private buffer. */
      sds ele;
      unsigned char *estr;
      unsigned int elen;
      long long ell;
      double score;
  } zsetopval;
  
  typedef union _iterset iterset;
  typedef union _iterzset iterzset;
  
  void zuiInitIterator(zsetopsrc *op) {
      if (op->subject == NULL)
          return;
  
      if (op->type == OBJ_SET) {
          iterset *it = &op->iter.set;
          if (op->encoding == OBJ_ENCODING_INTSET) {
              it->is.is = op->subject->ptr;
              it->is.ii = 0;
          } else if (op->encoding == OBJ_ENCODING_HT) {
              it->ht.dict = op->subject->ptr;
              it->ht.di = dictGetIterator(op->subject->ptr);
              it->ht.de = dictNext(it->ht.di);
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          iterzset *it = &op->iter.zset;
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              it->zl.zl = op->subject->ptr;
              it->zl.eptr = ziplistIndex(it->zl.zl,0);
              if (it->zl.eptr != NULL) {
                  it->zl.sptr = ziplistNext(it->zl.zl,it->zl.eptr);
                  serverAssert(it->zl.sptr != NULL);
              }
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              it->sl.zs = op->subject->ptr;
              it->sl.node = it->sl.zs->zsl->header->level[0].forward;
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
  }
  
  void zuiClearIterator(zsetopsrc *op) {
      if (op->subject == NULL)
          return;
  
      if (op->type == OBJ_SET) {
          iterset *it = &op->iter.set;
          if (op->encoding == OBJ_ENCODING_INTSET) {
              UNUSED(it); /* skip */
          } else if (op->encoding == OBJ_ENCODING_HT) {
              dictReleaseIterator(it->ht.di);
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          iterzset *it = &op->iter.zset;
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              UNUSED(it); /* skip */
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              UNUSED(it); /* skip */
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
  }
  
  unsigned long zuiLength(zsetopsrc *op) {
      if (op->subject == NULL)
          return 0;
  
      if (op->type == OBJ_SET) {
          if (op->encoding == OBJ_ENCODING_INTSET) {
              return intsetLen(op->subject->ptr);
          } else if (op->encoding == OBJ_ENCODING_HT) {
              dict *ht = op->subject->ptr;
              return dictSize(ht);
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              return zzlLength(op->subject->ptr);
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              zset *zs = op->subject->ptr;
              return zs->zsl->length;
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
  }
  
  /* Check if the current value is valid. If so, store it in the passed structure
   * and move to the next element. If not valid, this means we have reached the
   * end of the structure and can abort. */
  int zuiNext(zsetopsrc *op, zsetopval *val) {
      if (op->subject == NULL)
          return 0;
  
      if (val->flags & OPVAL_DIRTY_SDS)
          sdsfree(val->ele);
  
      memset(val,0,sizeof(zsetopval));
  
      if (op->type == OBJ_SET) {
          iterset *it = &op->iter.set;
          if (op->encoding == OBJ_ENCODING_INTSET) {
              int64_t ell;
  
              if (!intsetGet(it->is.is,it->is.ii,&ell))
                  return 0;
              val->ell = ell;
              val->score = 1.0;
  
              /* Move to next element. */
              it->is.ii++;
          } else if (op->encoding == OBJ_ENCODING_HT) {
              if (it->ht.de == NULL)
                  return 0;
              val->ele = dictGetKey(it->ht.de);
              val->score = 1.0;
  
              /* Move to next element. */
              it->ht.de = dictNext(it->ht.di);
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          iterzset *it = &op->iter.zset;
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              /* No need to check both, but better be explicit. */
              if (it->zl.eptr == NULL || it->zl.sptr == NULL)
                  return 0;
              serverAssert(ziplistGet(it->zl.eptr,&val->estr,&val->elen,&val->ell));
              val->score = zzlGetScore(it->zl.sptr);
  
              /* Move to next element. */
              zzlNext(it->zl.zl,&it->zl.eptr,&it->zl.sptr);
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              if (it->sl.node == NULL)
                  return 0;
              val->ele = it->sl.node->ele;
              val->score = it->sl.node->score;
  
              /* Move to next element. */
              it->sl.node = it->sl.node->level[0].forward;
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
      return 1;
  }
  
  int zuiLongLongFromValue(zsetopval *val) {
      if (!(val->flags & OPVAL_DIRTY_LL)) {
          val->flags |= OPVAL_DIRTY_LL;
  
          if (val->ele != NULL) {
              if (string2ll(val->ele,sdslen(val->ele),&val->ell))
                  val->flags |= OPVAL_VALID_LL;
          } else if (val->estr != NULL) {
              if (string2ll((char*)val->estr,val->elen,&val->ell))
                  val->flags |= OPVAL_VALID_LL;
          } else {
              /* The long long was already set, flag as valid. */
              val->flags |= OPVAL_VALID_LL;
          }
      }
      return val->flags & OPVAL_VALID_LL;
  }
  
  sds zuiSdsFromValue(zsetopval *val) {
      if (val->ele == NULL) {
          if (val->estr != NULL) {
              val->ele = sdsnewlen((char*)val->estr,val->elen);
          } else {
              val->ele = sdsfromlonglong(val->ell);
          }
          val->flags |= OPVAL_DIRTY_SDS;
      }
      return val->ele;
  }
  
  /* This is different from zuiSdsFromValue since returns a new SDS string
   * which is up to the caller to free. */
  sds zuiNewSdsFromValue(zsetopval *val) {
      if (val->flags & OPVAL_DIRTY_SDS) {
          /* We have already one to return! */
          sds ele = val->ele;
          val->flags &= ~OPVAL_DIRTY_SDS;
          val->ele = NULL;
          return ele;
      } else if (val->ele) {
          return sdsdup(val->ele);
      } else if (val->estr) {
          return sdsnewlen((char*)val->estr,val->elen);
      } else {
          return sdsfromlonglong(val->ell);
      }
  }
  
  int zuiBufferFromValue(zsetopval *val) {
      if (val->estr == NULL) {
          if (val->ele != NULL) {
              val->elen = sdslen(val->ele);
              val->estr = (unsigned char*)val->ele;
          } else {
              val->elen = ll2string((char*)val->_buf,sizeof(val->_buf),val->ell);
              val->estr = val->_buf;
          }
      }
      return 1;
  }
  
  /* Find value pointed to by val in the source pointer to by op. When found,
   * return 1 and store its score in target. Return 0 otherwise. */
  int zuiFind(zsetopsrc *op, zsetopval *val, double *score) {
      if (op->subject == NULL)
          return 0;
  
      if (op->type == OBJ_SET) {
          if (op->encoding == OBJ_ENCODING_INTSET) {
              if (zuiLongLongFromValue(val) &&
                  intsetFind(op->subject->ptr,val->ell))
              {
                  *score = 1.0;
                  return 1;
              } else {
                  return 0;
              }
          } else if (op->encoding == OBJ_ENCODING_HT) {
              dict *ht = op->subject->ptr;
              zuiSdsFromValue(val);
              if (dictFind(ht,val->ele) != NULL) {
                  *score = 1.0;
                  return 1;
              } else {
                  return 0;
              }
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          zuiSdsFromValue(val);
  
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              if (zzlFind(op->subject->ptr,val->ele,score) != NULL) {
                  /* Score is already set by zzlFind. */
                  return 1;
              } else {
                  return 0;
              }
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              zset *zs = op->subject->ptr;
              dictEntry *de;
              if ((de = dictFind(zs->dict,val->ele)) != NULL) {
                  *score = *(double*)dictGetVal(de);
                  return 1;
              } else {
                  return 0;
              }
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
  }
  
  int zuiCompareByCardinality(const void *s1, const void *s2) {
      unsigned long first = zuiLength((zsetopsrc*)s1);
      unsigned long second = zuiLength((zsetopsrc*)s2);
      if (first > second) return 1;
      if (first < second) return -1;
      return 0;
  }
  
  #define REDIS_AGGR_SUM 1
  #define REDIS_AGGR_MIN 2
  #define REDIS_AGGR_MAX 3
  #define zunionInterDictValue(_e) (dictGetVal(_e) == NULL ? 1.0 : *(double*)dictGetVal(_e))
  
  inline static void zunionInterAggregate(double *target, double val, int aggregate) {
      if (aggregate == REDIS_AGGR_SUM) {
          *target = *target + val;
          /* The result of adding two doubles is NaN when one variable
           * is +inf and the other is -inf. When these numbers are added,
           * we maintain the convention of the result being 0.0. */
          if (isnan(*target)) *target = 0.0;
      } else if (aggregate == REDIS_AGGR_MIN) {
          *target = val < *target ? val : *target;
      } else if (aggregate == REDIS_AGGR_MAX) {
          *target = val > *target ? val : *target;
      } else {
          /* safety net */
          serverPanic("Unknown ZUNION/INTER aggregate type");
      }
  }
  
  uint64_t dictSdsHash(const void *key);
  int dictSdsKeyCompare(void *privdata, const void *key1, const void *key2);
  
  dictType setAccumulatorDictType = {
      dictSdsHash,               /* hash function */
      NULL,                      /* key dup */
      NULL,                      /* val dup */
      dictSdsKeyCompare,         /* key compare */
      NULL,                      /* key destructor */
      NULL                       /* val destructor */
  };
  
  void zunionInterGenericCommand(client *c, robj *dstkey, int op) {
      int i, j;
      long setnum;
      int aggregate = REDIS_AGGR_SUM;
      zsetopsrc *src;
      zsetopval zval;
      sds tmp;
      size_t maxelelen = 0;
      robj *dstobj;
      zset *dstzset;
      zskiplistNode *znode;
      int touched = 0;
  
      /* expect setnum input keys to be given */
      if ((getLongFromObjectOrReply(c, c->argv[2], &setnum, NULL) != C_OK))
          return;
  
      if (setnum < 1) {
          addReplyError(c,
              "at least 1 input key is needed for ZUNIONSTORE/ZINTERSTORE");
          return;
      }
  
      /* test if the expected number of keys would overflow */
      if (setnum > c->argc-3) {
          addReply(c,shared.syntaxerr);
          return;
      }
  
      /* read keys to be used for input */
      src = zcalloc(sizeof(zsetopsrc) * setnum);
      for (i = 0, j = 3; i < setnum; i++, j++) {
          robj *obj = lookupKeyWrite(c->db,c->argv[j]);
          if (obj != NULL) {
              if (obj->type != OBJ_ZSET && obj->type != OBJ_SET) {
                  zfree(src);
                  addReply(c,shared.wrongtypeerr);
                  return;
              }
  
              src[i].subject = obj;
              src[i].type = obj->type;
              src[i].encoding = obj->encoding;
          } else {
              src[i].subject = NULL;
          }
  
          /* Default all weights to 1. */
          src[i].weight = 1.0;
      }
  
      /* parse optional extra arguments */
      if (j < c->argc) {
          int remaining = c->argc - j;
  
          while (remaining) {
              if (remaining >= (setnum + 1) &&
                  !strcasecmp(c->argv[j]->ptr,"weights"))
              {
                  j++; remaining--;
                  for (i = 0; i < setnum; i++, j++, remaining--) {
                      if (getDoubleFromObjectOrReply(c,c->argv[j],&src[i].weight,
                              "weight value is not a float") != C_OK)
                      {
                          zfree(src);
                          return;
                      }
                  }
              } else if (remaining >= 2 &&
                         !strcasecmp(c->argv[j]->ptr,"aggregate"))
              {
                  j++; remaining--;
                  if (!strcasecmp(c->argv[j]->ptr,"sum")) {
                      aggregate = REDIS_AGGR_SUM;
                  } else if (!strcasecmp(c->argv[j]->ptr,"min")) {
                      aggregate = REDIS_AGGR_MIN;
                  } else if (!strcasecmp(c->argv[j]->ptr,"max")) {
                      aggregate = REDIS_AGGR_MAX;
                  } else {
                      zfree(src);
                      addReply(c,shared.syntaxerr);
                      return;
                  }
                  j++; remaining--;
              } else {
                  zfree(src);
                  addReply(c,shared.syntaxerr);
                  return;
              }
          }
      }
  
      /* sort sets from the smallest to largest, this will improve our
       * algorithm's performance */
      qsort(src,setnum,sizeof(zsetopsrc),zuiCompareByCardinality);
  
      dstobj = createZsetObject();
      dstzset = dstobj->ptr;
      memset(&zval, 0, sizeof(zval));
  
      if (op == SET_OP_INTER) {
          /* Skip everything if the smallest input is empty. */
          if (zuiLength(&src[0]) > 0) {
              /* Precondition: as src[0] is non-empty and the inputs are ordered
               * by size, all src[i > 0] are non-empty too. */
              zuiInitIterator(&src[0]);
              while (zuiNext(&src[0],&zval)) {
                  double score, value;
  
                  score = src[0].weight * zval.score;
                  if (isnan(score)) score = 0;
  
                  for (j = 1; j < setnum; j++) {
                      /* It is not safe to access the zset we are
                       * iterating, so explicitly check for equal object. */
                      if (src[j].subject == src[0].subject) {
                          value = zval.score*src[j].weight;
                          zunionInterAggregate(&score,value,aggregate);
                      } else if (zuiFind(&src[j],&zval,&value)) {
                          value *= src[j].weight;
                          zunionInterAggregate(&score,value,aggregate);
                      } else {
                          break;
                      }
                  }
  
                  /* Only continue when present in every input. */
                  if (j == setnum) {
                      tmp = zuiNewSdsFromValue(&zval);
                      znode = zslInsert(dstzset->zsl,score,tmp);
                      dictAdd(dstzset->dict,tmp,&znode->score);
                      if (sdslen(tmp) > maxelelen) maxelelen = sdslen(tmp);
                  }
              }
              zuiClearIterator(&src[0]);
          }
      } else if (op == SET_OP_UNION) {
          dict *accumulator = dictCreate(&setAccumulatorDictType,NULL);
          dictIterator *di;
          dictEntry *de, *existing;
          double score;
  
          if (setnum) {
              /* Our union is at least as large as the largest set.
               * Resize the dictionary ASAP to avoid useless rehashing. */
              dictExpand(accumulator,zuiLength(&src[setnum-1]));
          }
  
          /* Step 1: Create a dictionary of elements -> aggregated-scores
           * by iterating one sorted set after the other. */
          for (i = 0; i < setnum; i++) {
              if (zuiLength(&src[i]) == 0) continue;
  
              zuiInitIterator(&src[i]);
              while (zuiNext(&src[i],&zval)) {
                  /* Initialize value */
                  score = src[i].weight * zval.score;
                  if (isnan(score)) score = 0;
  
                  /* Search for this element in the accumulating dictionary. */
                  de = dictAddRaw(accumulator,zuiSdsFromValue(&zval),&existing);
                  /* If we don't have it, we need to create a new entry. */
                  if (!existing) {
                      tmp = zuiNewSdsFromValue(&zval);
                      /* Remember the longest single element encountered,
                       * to understand if it's possible to convert to ziplist
                       * at the end. */
                       if (sdslen(tmp) > maxelelen) maxelelen = sdslen(tmp);
                      /* Update the element with its initial score. */
                      dictSetKey(accumulator, de, tmp);
                      dictSetDoubleVal(de,score);
                  } else {
                      /* Update the score with the score of the new instance
                       * of the element found in the current sorted set.
                       *
                       * Here we access directly the dictEntry double
                       * value inside the union as it is a big speedup
                       * compared to using the getDouble/setDouble API. */
                      zunionInterAggregate(&existing->v.d,score,aggregate);
                  }
              }
              zuiClearIterator(&src[i]);
          }
  
          /* Step 2: convert the dictionary into the final sorted set. */
          di = dictGetIterator(accumulator);
  
          /* We now are aware of the final size of the resulting sorted set,
           * let's resize the dictionary embedded inside the sorted set to the
           * right size, in order to save rehashing time. */
          dictExpand(dstzset->dict,dictSize(accumulator));
  
          while((de = dictNext(di)) != NULL) {
              sds ele = dictGetKey(de);
              score = dictGetDoubleVal(de);
              znode = zslInsert(dstzset->zsl,score,ele);
              dictAdd(dstzset->dict,ele,&znode->score);
          }
          dictReleaseIterator(di);
          dictRelease(accumulator);
      } else {
          serverPanic("Unknown operator");
      }
  
      if (dbDelete(c->db,dstkey))
          touched = 1;
      if (dstzset->zsl->length) {
          zsetConvertToZiplistIfNeeded(dstobj,maxelelen);
          dbAdd(c->db,dstkey,dstobj);
          addReplyLongLong(c,zsetLength(dstobj));
          signalModifiedKey(c,c->db,dstkey);
          notifyKeyspaceEvent(NOTIFY_ZSET,
              (op == SET_OP_UNION) ? "zunionstore" : "zinterstore",
              dstkey,c->db->id);
          server.dirty++;
      } else {
          decrRefCount(dstobj);
          addReply(c,shared.czero);
          if (touched) {
              signalModifiedKey(c,c->db,dstkey);
              notifyKeyspaceEvent(NOTIFY_GENERIC,"del",dstkey,c->db->id);
              server.dirty++;
          }
      }
      zfree(src);
  }
  
  void zunionstoreCommand(client *c) {
      zunionInterGenericCommand(c,c->argv[1], SET_OP_UNION);
  }
  
  void zinterstoreCommand(client *c) {
      zunionInterGenericCommand(c,c->argv[1], SET_OP_INTER);
  }
  
  void zrangeGenericCommand(client *c, int reverse) {
      robj *key = c->argv[1];
      robj *zobj;
      int withscores = 0;
      long start;
      long end;
      long llen;
      long rangelen;
  
      if ((getLongFromObjectOrReply(c, c->argv[2], &start, NULL) != C_OK) ||
          (getLongFromObjectOrReply(c, c->argv[3], &end, NULL) != C_OK)) return;
  
      if (c->argc == 5 && !strcasecmp(c->argv[4]->ptr,"withscores")) {
          withscores = 1;
      } else if (c->argc >= 5) {
          addReply(c,shared.syntaxerr);
          return;
      }
  
      if ((zobj = lookupKeyReadOrReply(c,key,shared.emptyarray)) == NULL
           || checkType(c,zobj,OBJ_ZSET)) return;
  
      /* Sanitize indexes. */
      llen = zsetLength(zobj);
      if (start < 0) start = llen+start;
      if (end < 0) end = llen+end;
      if (start < 0) start = 0;
  
      /* Invariant: start >= 0, so this test will be true when end < 0.
       * The range is empty when start > end or start >= length. */
      if (start > end || start >= llen) {
          addReply(c,shared.emptyarray);
          return;
      }
      if (end >= llen) end = llen-1;
      rangelen = (end-start)+1;
  
      /* Return the result in form of a multi-bulk reply. RESP3 clients
       * will receive sub arrays with score->element, while RESP2 returned
       * a flat array. */
      if (withscores && c->resp == 2)
          addReplyArrayLen(c, rangelen*2);
      else
          addReplyArrayLen(c, rangelen);
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
          unsigned char *vstr;
          unsigned int vlen;
          long long vlong;
  
          if (reverse)
              eptr = ziplistIndex(zl,-2-(2*start));
          else
              eptr = ziplistIndex(zl,2*start);
  
          serverAssertWithInfo(c,zobj,eptr != NULL);
          sptr = ziplistNext(zl,eptr);
  
          while (rangelen--) {
              serverAssertWithInfo(c,zobj,eptr != NULL && sptr != NULL);
              serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
  
              if (withscores && c->resp > 2) addReplyArrayLen(c,2);
              if (vstr == NULL)
                  addReplyBulkLongLong(c,vlong);
              else
                  addReplyBulkCBuffer(c,vstr,vlen);
              if (withscores) addReplyDouble(c,zzlGetScore(sptr));
  
              if (reverse)
                  zzlPrev(zl,&eptr,&sptr);
              else
                  zzlNext(zl,&eptr,&sptr);
          }
  
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *ln;
          sds ele;
  
          /* Check if starting point is trivial, before doing log(N) lookup. */
          if (reverse) {
              ln = zsl->tail;
              if (start > 0)
                  ln = zslGetElementByRank(zsl,llen-start);
          } else {
              ln = zsl->header->level[0].forward;
              if (start > 0)
                  ln = zslGetElementByRank(zsl,start+1);
          }
  
          while(rangelen--) {
              serverAssertWithInfo(c,zobj,ln != NULL);
              ele = ln->ele;
              if (withscores && c->resp > 2) addReplyArrayLen(c,2);
              addReplyBulkCBuffer(c,ele,sdslen(ele));
              if (withscores) addReplyDouble(c,ln->score);
              ln = reverse ? ln->backward : ln->level[0].forward;
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  }
  
  void zrangeCommand(client *c) {
      zrangeGenericCommand(c,0);
  }
  
  void zrevrangeCommand(client *c) {
      zrangeGenericCommand(c,1);
  }
  
  /* This command implements ZRANGEBYSCORE, ZREVRANGEBYSCORE. */
  void genericZrangebyscoreCommand(client *c, int reverse) {
      zrangespec range;
      robj *key = c->argv[1];
      robj *zobj;
      long offset = 0, limit = -1;
      int withscores = 0;
      unsigned long rangelen = 0;
      void *replylen = NULL;
      int minidx, maxidx;
  
      /* Parse the range arguments. */
      if (reverse) {
          /* Range is given as [max,min] */
          maxidx = 2; minidx = 3;
      } else {
          /* Range is given as [min,max] */
          minidx = 2; maxidx = 3;
      }
  
      if (zslParseRange(c->argv[minidx],c->argv[maxidx],&range) != C_OK) {
          addReplyError(c,"min or max is not a float");
          return;
      }
  
      /* Parse optional extra arguments. Note that ZCOUNT will exactly have
       * 4 arguments, so we'll never enter the following code path. */
      if (c->argc > 4) {
          int remaining = c->argc - 4;
          int pos = 4;
  
          while (remaining) {
              if (remaining >= 1 && !strcasecmp(c->argv[pos]->ptr,"withscores")) {
                  pos++; remaining--;
                  withscores = 1;
              } else if (remaining >= 3 && !strcasecmp(c->argv[pos]->ptr,"limit")) {
                  if ((getLongFromObjectOrReply(c, c->argv[pos+1], &offset, NULL)
                          != C_OK) ||
                      (getLongFromObjectOrReply(c, c->argv[pos+2], &limit, NULL)
                          != C_OK))
                  {
                      return;
                  }
                  pos += 3; remaining -= 3;
              } else {
                  addReply(c,shared.syntaxerr);
                  return;
              }
          }
      }
  
      /* Ok, lookup the key and get the range */
      if ((zobj = lookupKeyReadOrReply(c,key,shared.emptyarray)) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
          unsigned char *vstr;
          unsigned int vlen;
          long long vlong;
          double score;
  
          /* If reversed, get the last node in range as starting point. */
          if (reverse) {
              eptr = zzlLastInRange(zl,&range);
          } else {
              eptr = zzlFirstInRange(zl,&range);
          }
  
          /* No "first" element in the specified interval. */
          if (eptr == NULL) {
              addReply(c,shared.emptyarray);
              return;
          }
  
          /* Get score pointer for the first element. */
          serverAssertWithInfo(c,zobj,eptr != NULL);
          sptr = ziplistNext(zl,eptr);
  
          /* We don't know in advance how many matching elements there are in the
           * list, so we push this object that will represent the multi-bulk
           * length in the output buffer, and will "fix" it later */
          replylen = addReplyDeferredLen(c);
  
          /* If there is an offset, just traverse the number of elements without
           * checking the score because that is done in the next loop. */
          while (eptr && offset--) {
              if (reverse) {
                  zzlPrev(zl,&eptr,&sptr);
              } else {
                  zzlNext(zl,&eptr,&sptr);
              }
          }
  
          while (eptr && limit--) {
              score = zzlGetScore(sptr);
  
              /* Abort when the node is no longer in range. */
              if (reverse) {
                  if (!zslValueGteMin(score,&range)) break;
              } else {
                  if (!zslValueLteMax(score,&range)) break;
              }
  
              /* We know the element exists, so ziplistGet should always
               * succeed */
              serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
  
              rangelen++;
              if (withscores && c->resp > 2) addReplyArrayLen(c,2);
              if (vstr == NULL) {
                  addReplyBulkLongLong(c,vlong);
              } else {
                  addReplyBulkCBuffer(c,vstr,vlen);
              }
              if (withscores) addReplyDouble(c,score);
  
              /* Move to next node */
              if (reverse) {
                  zzlPrev(zl,&eptr,&sptr);
              } else {
                  zzlNext(zl,&eptr,&sptr);
              }
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *ln;
  
          /* If reversed, get the last node in range as starting point. */
          if (reverse) {
              ln = zslLastInRange(zsl,&range);
          } else {
              ln = zslFirstInRange(zsl,&range);
          }
  
          /* No "first" element in the specified interval. */
          if (ln == NULL) {
              addReply(c,shared.emptyarray);
              return;
          }
  
          /* We don't know in advance how many matching elements there are in the
           * list, so we push this object that will represent the multi-bulk
           * length in the output buffer, and will "fix" it later */
          replylen = addReplyDeferredLen(c);
  
          /* If there is an offset, just traverse the number of elements without
           * checking the score because that is done in the next loop. */
          while (ln && offset--) {
              if (reverse) {
                  ln = ln->backward;
              } else {
                  ln = ln->level[0].forward;
              }
          }
  
          while (ln && limit--) {
              /* Abort when the node is no longer in range. */
              if (reverse) {
                  if (!zslValueGteMin(ln->score,&range)) break;
              } else {
                  if (!zslValueLteMax(ln->score,&range)) break;
              }
  
              rangelen++;
              if (withscores && c->resp > 2) addReplyArrayLen(c,2);
              addReplyBulkCBuffer(c,ln->ele,sdslen(ln->ele));
              if (withscores) addReplyDouble(c,ln->score);
  
              /* Move to next node */
              if (reverse) {
                  ln = ln->backward;
              } else {
                  ln = ln->level[0].forward;
              }
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      if (withscores && c->resp == 2) rangelen *= 2;
      setDeferredArrayLen(c, replylen, rangelen);
  }
  
  void zrangebyscoreCommand(client *c) {
      genericZrangebyscoreCommand(c,0);
  }
  
  void zrevrangebyscoreCommand(client *c) {
      genericZrangebyscoreCommand(c,1);
  }
  
  void zcountCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
      zrangespec range;
      unsigned long count = 0;
  
      /* Parse the range arguments */
      if (zslParseRange(c->argv[2],c->argv[3],&range) != C_OK) {
          addReplyError(c,"min or max is not a float");
          return;
      }
  
      /* Lookup the sorted set */
      if ((zobj = lookupKeyReadOrReply(c, key, shared.czero)) == NULL ||
          checkType(c, zobj, OBJ_ZSET)) return;
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
          double score;
  
          /* Use the first element in range as the starting point */
          eptr = zzlFirstInRange(zl,&range);
  
          /* No "first" element */
          if (eptr == NULL) {
              addReply(c, shared.czero);
              return;
          }
  
          /* First element is in range */
          sptr = ziplistNext(zl,eptr);
          score = zzlGetScore(sptr);
          serverAssertWithInfo(c,zobj,zslValueLteMax(score,&range));
  
          /* Iterate over elements in range */
          while (eptr) {
              score = zzlGetScore(sptr);
  
              /* Abort when the node is no longer in range. */
              if (!zslValueLteMax(score,&range)) {
                  break;
              } else {
                  count++;
                  zzlNext(zl,&eptr,&sptr);
              }
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *zn;
          unsigned long rank;
  
          /* Find first element in range */
          zn = zslFirstInRange(zsl, &range);
  
          /* Use rank of first element, if any, to determine preliminary count */
          if (zn != NULL) {
              rank = zslGetRank(zsl, zn->score, zn->ele);
              count = (zsl->length - (rank - 1));
  
              /* Find last element in range */
              zn = zslLastInRange(zsl, &range);
  
              /* Use rank of last element, if any, to determine the actual count */
              if (zn != NULL) {
                  rank = zslGetRank(zsl, zn->score, zn->ele);
                  count -= (zsl->length - rank);
              }
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      addReplyLongLong(c, count);
  }
  
  void zlexcountCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
      zlexrangespec range;
      unsigned long count = 0;
  
      /* Parse the range arguments */
      if (zslParseLexRange(c->argv[2],c->argv[3],&range) != C_OK) {
          addReplyError(c,"min or max not valid string range item");
          return;
      }
  
      /* Lookup the sorted set */
      if ((zobj = lookupKeyReadOrReply(c, key, shared.czero)) == NULL ||
          checkType(c, zobj, OBJ_ZSET))
      {
          zslFreeLexRange(&range);
          return;
      }
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
  
          /* Use the first element in range as the starting point */
          eptr = zzlFirstInLexRange(zl,&range);
  
          /* No "first" element */
          if (eptr == NULL) {
              zslFreeLexRange(&range);
              addReply(c, shared.czero);
              return;
          }
  
          /* First element is in range */
          sptr = ziplistNext(zl,eptr);
          serverAssertWithInfo(c,zobj,zzlLexValueLteMax(eptr,&range));
  
          /* Iterate over elements in range */
          while (eptr) {
              /* Abort when the node is no longer in range. */
              if (!zzlLexValueLteMax(eptr,&range)) {
                  break;
              } else {
                  count++;
                  zzlNext(zl,&eptr,&sptr);
              }
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *zn;
          unsigned long rank;
  
          /* Find first element in range */
          zn = zslFirstInLexRange(zsl, &range);
  
          /* Use rank of first element, if any, to determine preliminary count */
          if (zn != NULL) {
              rank = zslGetRank(zsl, zn->score, zn->ele);
              count = (zsl->length - (rank - 1));
  
              /* Find last element in range */
              zn = zslLastInLexRange(zsl, &range);
  
              /* Use rank of last element, if any, to determine the actual count */
              if (zn != NULL) {
                  rank = zslGetRank(zsl, zn->score, zn->ele);
                  count -= (zsl->length - rank);
              }
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      zslFreeLexRange(&range);
      addReplyLongLong(c, count);
  }
  
  /* This command implements ZRANGEBYLEX, ZREVRANGEBYLEX. */
  void genericZrangebylexCommand(client *c, int reverse) {
      zlexrangespec range;
      robj *key = c->argv[1];
      robj *zobj;
      long offset = 0, limit = -1;
      unsigned long rangelen = 0;
      void *replylen = NULL;
      int minidx, maxidx;
  
      /* Parse the range arguments. */
      if (reverse) {
          /* Range is given as [max,min] */
          maxidx = 2; minidx = 3;
      } else {
          /* Range is given as [min,max] */
          minidx = 2; maxidx = 3;
      }
  
      if (zslParseLexRange(c->argv[minidx],c->argv[maxidx],&range) != C_OK) {
          addReplyError(c,"min or max not valid string range item");
          return;
      }
  
      /* Parse optional extra arguments. Note that ZCOUNT will exactly have
       * 4 arguments, so we'll never enter the following code path. */
      if (c->argc > 4) {
          int remaining = c->argc - 4;
          int pos = 4;
  
          while (remaining) {
              if (remaining >= 3 && !strcasecmp(c->argv[pos]->ptr,"limit")) {
                  if ((getLongFromObjectOrReply(c, c->argv[pos+1], &offset, NULL) != C_OK) ||
                      (getLongFromObjectOrReply(c, c->argv[pos+2], &limit, NULL) != C_OK)) {
                      zslFreeLexRange(&range);
                      return;
                  }
                  pos += 3; remaining -= 3;
              } else {
                  zslFreeLexRange(&range);
                  addReply(c,shared.syntaxerr);
                  return;
              }
          }
      }
  
      /* Ok, lookup the key and get the range */
      if ((zobj = lookupKeyReadOrReply(c,key,shared.emptyarray)) == NULL ||
          checkType(c,zobj,OBJ_ZSET))
      {
          zslFreeLexRange(&range);
          return;
      }
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
          unsigned char *vstr;
          unsigned int vlen;
          long long vlong;
  
          /* If reversed, get the last node in range as starting point. */
          if (reverse) {
              eptr = zzlLastInLexRange(zl,&range);
          } else {
              eptr = zzlFirstInLexRange(zl,&range);
          }
  
          /* No "first" element in the specified interval. */
          if (eptr == NULL) {
              addReply(c,shared.emptyarray);
              zslFreeLexRange(&range);
              return;
          }
  
          /* Get score pointer for the first element. */
          serverAssertWithInfo(c,zobj,eptr != NULL);
          sptr = ziplistNext(zl,eptr);
  
          /* We don't know in advance how many matching elements there are in the
           * list, so we push this object that will represent the multi-bulk
           * length in the output buffer, and will "fix" it later */
          replylen = addReplyDeferredLen(c);
  
          /* If there is an offset, just traverse the number of elements without
           * checking the score because that is done in the next loop. */
          while (eptr && offset--) {
              if (reverse) {
                  zzlPrev(zl,&eptr,&sptr);
              } else {
                  zzlNext(zl,&eptr,&sptr);
              }
          }
  
          while (eptr && limit--) {
              /* Abort when the node is no longer in range. */
              if (reverse) {
                  if (!zzlLexValueGteMin(eptr,&range)) break;
              } else {
                  if (!zzlLexValueLteMax(eptr,&range)) break;
              }
  
              /* We know the element exists, so ziplistGet should always
               * succeed. */
              serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
  
              rangelen++;
              if (vstr == NULL) {
                  addReplyBulkLongLong(c,vlong);
              } else {
                  addReplyBulkCBuffer(c,vstr,vlen);
              }
  
              /* Move to next node */
              if (reverse) {
                  zzlPrev(zl,&eptr,&sptr);
              } else {
                  zzlNext(zl,&eptr,&sptr);
              }
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *ln;
  
          /* If reversed, get the last node in range as starting point. */
          if (reverse) {
              ln = zslLastInLexRange(zsl,&range);
          } else {
              ln = zslFirstInLexRange(zsl,&range);
          }
  
          /* No "first" element in the specified interval. */
          if (ln == NULL) {
              addReply(c,shared.emptyarray);
              zslFreeLexRange(&range);
              return;
          }
  
          /* We don't know in advance how many matching elements there are in the
           * list, so we push this object that will represent the multi-bulk
           * length in the output buffer, and will "fix" it later */
          replylen = addReplyDeferredLen(c);
  
          /* If there is an offset, just traverse the number of elements without
           * checking the score because that is done in the next loop. */
          while (ln && offset--) {
              if (reverse) {
                  ln = ln->backward;
              } else {
                  ln = ln->level[0].forward;
              }
          }
  
          while (ln && limit--) {
              /* Abort when the node is no longer in range. */
              if (reverse) {
                  if (!zslLexValueGteMin(ln->ele,&range)) break;
              } else {
                  if (!zslLexValueLteMax(ln->ele,&range)) break;
              }
  
              rangelen++;
              addReplyBulkCBuffer(c,ln->ele,sdslen(ln->ele));
  
              /* Move to next node */
              if (reverse) {
                  ln = ln->backward;
              } else {
                  ln = ln->level[0].forward;
              }
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      zslFreeLexRange(&range);
      setDeferredArrayLen(c, replylen, rangelen);
  }
  
  void zrangebylexCommand(client *c) {
      genericZrangebylexCommand(c,0);
  }
  
  void zrevrangebylexCommand(client *c) {
      genericZrangebylexCommand(c,1);
  }
  
  void zcardCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
  
      if ((zobj = lookupKeyReadOrReply(c,key,shared.czero)) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      addReplyLongLong(c,zsetLength(zobj));
  }
  
  void zscoreCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
      double score;
  
      if ((zobj = lookupKeyReadOrReply(c,key,shared.null[c->resp])) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      if (zsetScore(zobj,c->argv[2]->ptr,&score) == C_ERR) {
          addReplyNull(c);
      } else {
          addReplyDouble(c,score);
      }
  }
  
  void zrankGenericCommand(client *c, int reverse) {
      robj *key = c->argv[1];
      robj *ele = c->argv[2];
      robj *zobj;
      long rank;
  
      if ((zobj = lookupKeyReadOrReply(c,key,shared.null[c->resp])) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      serverAssertWithInfo(c,ele,sdsEncodedObject(ele));
      rank = zsetRank(zobj,ele->ptr,reverse);
      if (rank >= 0) {
          addReplyLongLong(c,rank);
      } else {
          addReplyNull(c);
      }
  }
  
  void zrankCommand(client *c) {
      zrankGenericCommand(c, 0);
  }
  
  void zrevrankCommand(client *c) {
      zrankGenericCommand(c, 1);
  }
  
  void zscanCommand(client *c) {
      robj *o;
      unsigned long cursor;
  
      if (parseScanCursorOrReply(c,c->argv[2],&cursor) == C_ERR) return;
      if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.emptyscan)) == NULL ||
          checkType(c,o,OBJ_ZSET)) return;
      scanGenericCommand(c,o,cursor);
  }
  
  /* This command implements the generic zpop operation, used by:
   * ZPOPMIN, ZPOPMAX, BZPOPMIN and BZPOPMAX. This function is also used
   * inside blocked.c in the unblocking stage of BZPOPMIN and BZPOPMAX.
   *
   * If 'emitkey' is true also the key name is emitted, useful for the blocking
   * behavior of BZPOP[MIN|MAX], since we can block into multiple keys.
   *
   * The synchronous version instead does not need to emit the key, but may
   * use the 'count' argument to return multiple items if available. */
  void genericZpopCommand(client *c, robj **keyv, int keyc, int where, int emitkey, robj *countarg) {
      int idx;
      robj *key = NULL;
      robj *zobj = NULL;
      sds ele;
      double score;
      long count = 1;
  
      /* If a count argument as passed, parse it or return an error. */
      if (countarg) {
          if (getLongFromObjectOrReply(c,countarg,&count,NULL) != C_OK)
              return;
          if (count <= 0) {
              addReply(c,shared.emptyarray);
              return;
          }
      }
  
      /* Check type and break on the first error, otherwise identify candidate. */
      idx = 0;
      while (idx < keyc) {
          key = keyv[idx++];
          zobj = lookupKeyWrite(c->db,key);
          if (!zobj) continue;
          if (checkType(c,zobj,OBJ_ZSET)) return;
          break;
      }
  
      /* No candidate for zpopping, return empty. */
      if (!zobj) {
          addReply(c,shared.emptyarray);
          return;
      }
  
      void *arraylen_ptr = addReplyDeferredLen(c);
      long arraylen = 0;
  
      /* We emit the key only for the blocking variant. */
      if (emitkey) addReplyBulk(c,key);
  
      /* Remove the element. */
      do {
          if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
              unsigned char *zl = zobj->ptr;
              unsigned char *eptr, *sptr;
              unsigned char *vstr;
              unsigned int vlen;
              long long vlong;
  
              /* Get the first or last element in the sorted set. */
              eptr = ziplistIndex(zl,where == ZSET_MAX ? -2 : 0);
              serverAssertWithInfo(c,zobj,eptr != NULL);
              serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
              if (vstr == NULL)
                  ele = sdsfromlonglong(vlong);
              else
                  ele = sdsnewlen(vstr,vlen);
  
              /* Get the score. */
              sptr = ziplistNext(zl,eptr);
              serverAssertWithInfo(c,zobj,sptr != NULL);
              score = zzlGetScore(sptr);
          } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
              zset *zs = zobj->ptr;
              zskiplist *zsl = zs->zsl;
              zskiplistNode *zln;
  
              /* Get the first or last element in the sorted set. */
              zln = (where == ZSET_MAX ? zsl->tail :
                                         zsl->header->level[0].forward);
  
              /* There must be an element in the sorted set. */
              serverAssertWithInfo(c,zobj,zln != NULL);
              ele = sdsdup(zln->ele);
              score = zln->score;
          } else {
              serverPanic("Unknown sorted set encoding");
          }
  
          serverAssertWithInfo(c,zobj,zsetDel(zobj,ele));
          server.dirty++;
  
          if (arraylen == 0) { /* Do this only for the first iteration. */
              char *events[2] = {"zpopmin","zpopmax"};
              notifyKeyspaceEvent(NOTIFY_ZSET,events[where],key,c->db->id);
              signalModifiedKey(c,c->db,key);
          }
  
          addReplyBulkCBuffer(c,ele,sdslen(ele));
          addReplyDouble(c,score);
          sdsfree(ele);
          arraylen += 2;
  
          /* Remove the key, if indeed needed. */
          if (zsetLength(zobj) == 0) {
              dbDelete(c->db,key);
              notifyKeyspaceEvent(NOTIFY_GENERIC,"del",key,c->db->id);
              break;
          }
      } while(--count);
  
      setDeferredArrayLen(c,arraylen_ptr,arraylen + (emitkey != 0));
  }
  
  /* ZPOPMIN key [<count>] */
  void zpopminCommand(client *c) {
      if (c->argc > 3) {
          addReply(c,shared.syntaxerr);
          return;
      }
      genericZpopCommand(c,&c->argv[1],1,ZSET_MIN,0,
          c->argc == 3 ? c->argv[2] : NULL);
  }
  
  /* ZMAXPOP key [<count>] */
  void zpopmaxCommand(client *c) {
      if (c->argc > 3) {
          addReply(c,shared.syntaxerr);
          return;
      }
      genericZpopCommand(c,&c->argv[1],1,ZSET_MAX,0,
          c->argc == 3 ? c->argv[2] : NULL);
  }
  
  /* BZPOPMIN / BZPOPMAX actual implementation. */
  void blockingGenericZpopCommand(client *c, int where) {
      robj *o;
      mstime_t timeout;
      int j;
  
      if (getTimeoutFromObjectOrReply(c,c->argv[c->argc-1],&timeout,UNIT_SECONDS)
          != C_OK) return;
  
      for (j = 1; j < c->argc-1; j++) {
          o = lookupKeyWrite(c->db,c->argv[j]);
          if (o != NULL) {
              if (o->type != OBJ_ZSET) {
                  addReply(c,shared.wrongtypeerr);
                  return;
              } else {
                  if (zsetLength(o) != 0) {
                      /* Non empty zset, this is like a normal ZPOP[MIN|MAX]. */
                      genericZpopCommand(c,&c->argv[j],1,where,1,NULL);
                      /* Replicate it as an ZPOP[MIN|MAX] instead of BZPOP[MIN|MAX]. */
                      rewriteClientCommandVector(c,2,
                          where == ZSET_MAX ? shared.zpopmax : shared.zpopmin,
                          c->argv[j]);
                      return;
                  }
              }
          }
      }
  
      /* If we are inside a MULTI/EXEC and the zset is empty the only thing
       * we can do is treating it as a timeout (even with timeout 0). */
      if (c->flags & CLIENT_MULTI) {
          addReplyNullArray(c);
          return;
      }
  
      /* If the keys do not exist we must block */
      blockForKeys(c,BLOCKED_ZSET,c->argv + 1,c->argc - 2,timeout,NULL,NULL);
  }
  
  // BZPOPMIN key [key ...] timeout
  void bzpopminCommand(client *c) {
      blockingGenericZpopCommand(c,ZSET_MIN);
  }
  
  // BZPOPMAX key [key ...] timeout
  void bzpopmaxCommand(client *c) {
      blockingGenericZpopCommand(c,ZSET_MAX);
  }
  